Decentralized Applications (Dapps) Coursera Quiz Answers

All Weeks Decentralized Applications (Dapps) Coursera Quiz Answers

This third course of the Blockchain specialization prepares you to design and develop end-to-end decentralized applications (Dapps) – which provide anyone with access to the blockchain’s features and services.

The course covers the basic design of a Dapp, Truffle development process, and commands (init, develop, test, and migrate), test-driven development of Dapp, Dapp application models, and emerging standards that are essential for predictable Dapp behavior.

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Decentralized Applications (Dapps) Week 1 Quiz Answers

Quiz 1: Self-Check

Q1. What does the following figure represent?

  • Dapp stack
  • Service layer
  • Server
  • Blockchain stack

Q2. Blockchain server provides access to infrastructure hardware and blockchain services. True or False?

  • False
  • True

Q3. What does the enode address represent?

  • Addresses of the ethereum accounts
  • Hash of your accounts
  • Address of the ethereum node
  • Address of the coinbase

Q4. What is the use of enode address?

  • Used by account to receive money from others
  • Used by nodes to connect and form a p2p network
  • Used by account to send money to others
  • Used by the system to communicate with its coinbase

Quiz 2: Self-Check

Q1. What is the CLI command used to send ethers after the nodes have been initialized?

  • eth.submitTransaction()
  • eth.sendRawTransaction()
  • eth.sendTransaction()
  • eth.sendIBANTransaction()

Q2. In this lesson, what port do we expose the RPC for the Ethereum network on?

  • 8544
  • 8545
  • 7545
  • 9545

Q3. To access smart contracts from the Dapp web interfaces we need the Web3 script. True or False?

  • False
  • True

Quiz 3: Self-Check

Q1. What does API stand for?

  • Application Protocol Interface
  • Automatic Process Initiator
  • Application Performance Indicator
  • Application Programming Interface

Q2. Which of these are Ethereum APIs?

  • eth
  • admin
  • enode
  • miner

Q3. What library/API is used for smart contract deployment and invocation from Dapp ?

  • web3
  • contract
  • eth
  • admin

Quiz 4: Decentralized Applications (Dapps) – Week 1

Q1. For a web application we associate a web server, for a mobile application we associate a mobile server. For a decentralized application we associate a ____.

  • Distributed communication server
  • Blockchain server
  • Distributed application server
  • Centralized Server

Q2. What is the network id for Ethereum’s testnet server, Rinkeby?

  • 1
  • 2
  • 3
  • 4

Q3. What does the web3 library do to help DApps to communicate with the ethereum network?

  • SOAP Requests
  • RPC Calls
  • REST Requests
  • POST Requests

Q4. Which is one of the main use of APIs?

  • Providing access to data and services
  • Deploying smart contracts
  • VoIP services
  • Build DApp front ends

Q5. Which of these APIs you can use to see the nodes connected to the network?

  • admin.peers()
  • admin.nodeInfo()
  • eth.viewPeers()
  • admin.stats()

Q6. Which API can you use to start mining on your computer once a node is setup?

  • user.startMiner()
  • admin.startMiner()
  • miner.start()
  • eth.startMiner()

Q7. Which of these APIs can you use to create a new account on the Ethereum network?

  • user.createAccount()
  • user.newAccount()
  • personal.createAccount()
  • personal.newAccount()

Q8. You can use the Eth API to view your balance. Which of these functions would you call to do that?

  • eth.getBalance()
  • eth.viewBalance()
  • eth.balance()
  • eth.myBalance()

Decentralized Applications (Dapps) Week 2 Quiz Answers

Quiz 1: Self-Check

Q1. What are the steps in Dapp development process?

  • Analyze problem, prototype smart contract on remix, develop and test in truffle
  • Prototype smart contract on remix, develop and test in truffle, deploy
  • Analyze problem, develop and test in truffle, deploy
  • Analyze problem, prototype smart contract on remix, develop and test in truffle, deploy

Q2. What does truffle init do?

  • Starts the truffle network for you
  • Downloads a sample Dapp
  • Creates a base directory and initializes templates with base Dapp code
  • Connects to node running in your local

Q3. What is the RPC port for test chain deployed by “truffle develop”?

  • 8545
  • 8544
  • 7545
  • 9545

Q4. What does the option –reset in truffle migrate do?

  • Runs the latest migration
  • Run all migrations from beginning
  • Clears the intermediate transactions
  • Start execution from the last but one migration

Quiz 2: Self-Check

Q1. What is a positive test case in test-driven development?

  • You provide valid values for input and test passes if the system behavior is correct and valid for the given input
  • You provide invalid values for input and test passes if the system behavior is correct and valid
  • You provide valid values for input and test passes if the system behavior is incorrect and invalid for the given input
  • You provide invalid values for input and test passes if the system behavior is incorrect and invalid

Q2. What is the command for running test scripts ?

  • truffle test.js
  • test test.js
  • truffle test
  • test truffle

Q3. What is a negative test case in test-driven development?

  • You provide valid values for input and test passes if the system behavior is correct and valid for the given input
  • You provide invalid values for input and test fails
  • You provide valid values for input and test passes if the system behavior is incorrect and invalid for the given input
  • You provide invalid values for input and test passes if the system catches and flags the invalid inputs

Quiz 3: Self-Check

Q1. What role does app.js play in the Dapp design?

  • Instantiates object needed for the web client to communicate with the blockchain node
  • Deploys smart contracts
  • Handles business logic of Dapp
  • Initiates the blockchain network

Q2. How are accounts in the test chain created by truffle develop connected to the Dapp?

  • Ganache
  • Truffle CLI
  • Metamask
  • Web3 script

Q3. What is the command to start web server for the Dapp in our lesson?

  • npm run dev
  • npm start server
  • npm start
  • npm dev run

Quiz 4: Truffle Development – Week 2

Q1. Once you initialize a Truffle directory, the default directory structure contains which of the following?

  • contracts/ – containing the Solidity source files for our smart contracts.
  • migrations/ – to handle smart contract deployment.
  • test/ – contains both JavaScript and Solidity tests.
  • All of the above.

Q2. How do you interact with accounts of a Dapp from a browser?

  • Through Ganache
  • Through Remix
  • Through MetaMask
  • Through Oraclize

Q3. In what language is the test program for testing the Ballot2 Dapp written in the lesson discussed?

  • Python
  • Solidity
  • Java
  • Javascript

Q4. What is the benefit of writing the test program in Javascipt over Solidity language?

  • JS can handle Smart Contract addresses
  • JS is easy to code
  • JS is used in web programming

Q5. What can you use to create an empty truffle project?

  • truffle init
  • truffle start
  • truffle create
  • truffle compile

Q6. What command is used to convert solidity code to byte code for the EVM to execute?

  • truffle convert2byte
  • truffle convert
  • truffle compile
  • truffle execute

Q7. What can you use to deploy truffle’s built-in blockchain test chain?

  • truffle switch
  • truffle init
  • truffle develop
  • truffle compile

Q8. What command is used to redeploy Dapp’s contracts?

  • truffle develop
  • truffle compile
  • truffle alter
  • truffle migrate –reset

Q9. How can you test your smart contracts on truffle?

  • truffle test
  • truffle test_contract
  • truffle contract
  • truffle test contract

Decentralized Applications (Dapps) Week 3 Quiz Answers

Quiz 1: Self-Check

Q1. What type of variable is assigned to a local array inside a function by default?

  • storage
  • referenced
  • persistent
  • memory

Q2. How is a smart contract identified?

  • Its name
  • Its address
  • Deployer’s address
  • ABI

Q3. You can not change the ownership of a smart contract

  • True
  • False

Q4. Using which keyword you associate an interface with a smart contract

  • pragma
  • contract
  • import
  • library

Quiz 2: Self-Check

Q1. How is an event defined?

  • They are defined same as functions
  • They are defined as a state inside the contract
  • They are defined with name and parameters

Q2. In the Coin Dapp we discussed, what is event sent used for?

  • Pushing a notification that coins have been transferred between sender and receiver
  • To invoke eth.sendTransaction() from front end
  • For debugging purpose
  • Sending coins from sender to receiver

Q3. What are the parameters for the sent event in coin smart contract?

  • Address from, Address to, uint Amount
  • Address to, uint Amount
  • uint from, uint to, uint Amount
  • String from, String to, uint Amount

Q4. What is an event used for?

  • For debugging purpose
  • Sending coins from sender to receiver
  • Pushing smart contract state changes to any monitoring applications
  • To invoke eth.sendTransaction() from front end

Quiz 3: Self-Check

Q1. What is the purpose of a callback function, when using Oraclize?

  • Batch processing of data request
  • Synchronous processing of data request
  • Asynchronous processing of data request
  • To send data request to Oraclize

Q2. What is Oraclize as described in the lesson?

  • Means for smart contracts to access data from external sources securely
  • Means for smart contracts to push data to external sources securely
  • To check if a smart contract is mined and confirmed
  • Communication between two different blockchain network

Quiz 4: Design Improvements – Week 3

Q1. How can smart contracts access the data from different websites or APIs?

  • By using Truffle
  • By requesting the websites directly for the data
  • It’s not possible for the smart contracts to access the data
  • By using Oraclize

Q2. How can the blockchain applications trust the data response they get from Oraclize?

  • By accepting data inputs from more than one untrusted or partially trusted party and then executing the data-dependent action only after a number of them have provided the same answer.
  • Oraclize shows that the data is genuine by providing a document called authenticity proof along with the actual returned data.
  • None of the above.
  • By verifying from other third party sources.

Q3. Logs of events are stored in _______ .

  • Server node
  • One node
  • Client node
  • All nodes

Q4. What is the maximum number of parameters can be indexed for a given event specification?

  • No such limit
  • 2
  • 3
  • 1

Q5. Which of the following is true for using Libraries in blockchain?

  • Libraries are not stateless
  • Libraries can store ethers
  • Libraries can receive ethers
  • Libraries are stateless

Q6. By default which type of variable is assigned to arrays and structs in solidity smart contracts?

  • Memory or Storage depending on whether it is local or global
  • No default assignment of variable type
  • Memory variable
  • Storage variable

Q7. What happens when a contract calls selfdestruct ?

  • Remaining ethers are sent to a designated address and storage and code are removed from state
  • Contract becomes inaccessible at a given address
  • Contract can still be accessed but you can no longer send or receive ethers

Decentralized Applications (Dapps) Week 4 Quiz Answers

Quiz 1: Self-Check

Q1. What kind of Dapp did Bitcoin enable ?

  • P2P payment system
  • Anonymous payment system
  • Private payment system
  • Dysfunctional payment system

Q2. What is a DAO?

  • Decentralized Autonomous Oraclize
  • Autonomous Oraclize
  • Distributed Autonomous Organization
  • Decentralized Autonomous Organization

Q3. Is DAO a smart contract?

  • False
  • True

Q4. What are ICOs primarily used for ?

  • Trading
  • Comparing different coins
  • Fundraising
  • Solving business logics

Quiz 2: Self-Check

Q1. How do you make your token ERC 20 compliant?

  • Use the latest version of solidity compiler
  • Token smart contract must implement ERC 20 interface functions
  • ERC 20 smart contract must implement Token interface functions
  • Use ERC 20 tokens instead of ethers

Q2. Which of the following is true about ERC 20 and ERC 721 tokens?

  • ERC 20 is fungible, ERC 721 is non fungible
  • Both are fungible
  • ERC 20 is non fungible, ERC 721 is fungible
  • Both are non fungible

Q3. You can use a blockchain token to ____.

  • buy votes to be a chairman
  • quickly monetize an idea or service
  • enable mining

Q4. Token is a smart contract

  • True
  • False

Q5. Explain importance of standardization to Dapps.

  • So that they follow certain conventions
  • So that they can implement certain methods
  • So that they can all be the same

Q6. Which one of the following is ERC 20 compliant ?

  • REP
  • Coinbase
  • Exodus
  • Jaxx

Q7. On etherscan when you hover over a ERC 20 token such as SALT what message shows up?

  • Standard ERC-20 Token
  • ERC 721 Token
  • ERC Token Compliant

Quiz 3: Application Models & Standards – Week 4

Q1. What does EIP stand for?

  • Ethereum International Protocol
  • Ethereum Integration Proposal
  • Ethereum Improvement Protocol
  • Ethereum Improvement Proposal

Q2. What is ERC 20?

  • It is an EIP protocol which defines how to carry out transactions
  • It defines a common set of rules and functions for all ERC20 Ethereum tokens to follow, allowing easy integration of new tokens
  • It defines rules for the authentication and privacy of Ethereum transactions.
  • None

Q3. Review the ERC20 Interface from this link.​ Which are the functions below do you need to implement to make your token ERC 20 compliant? Select all the functions needed.

  • totalSupply()
  • balanceOf()
  • transfer()
  • approve()

Q4. What does ERC stand for?

  • Ethereum Replacement of Code
  • Ethereum Requisite for Code
  • Ethereum Request for Comments
  • Ethereum Revision Comments

Q5. Which of the following is true regarding a fungible token?

  • Its intrinsic value can change
  • It is not mutually interchangeable1:1 to another of its kind
  • It is a mutually interchangeable 1:1 to another of its kind

Q6. What is a famous example of a nonfungible token?

  • Cryptokitties
  • Zcash
  • Augur
  • US Dollar

Q7. What is ICO?

  • Independent Coin Offering
  • Initial Coin Offering
  • Inferred Coin Offering
  • Independent Code Ordering

Q8. What significant event did Ethereum Decentralized Autonomous Organization (DAO) precipitate?

  • Change of consensus algorithm
  • Hard fork of Ethereum
  • Soft fork of Ethereum
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All Course Quiz Answers of Blockchain Specialization

Course 01: Blockchain Basics

Course 02: Smart Contracts

Course 03: Decentralized Applications (Dapps)

Course 04: Blockchain Platforms

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