FREE Certified Blockchain Professional (CBCP) Smart Contracts and dApps Questions and Answers

Question 1

A smart contract for a decentralized insurance dApp needs to automatically process a claim based on the real-world occurrence of a hurricane.
Since the blockchain cannot directly access external weather data, what component is essential for the smart contract to receive this information securely and reliably?

Accepted Answer

A decentralized oracle network to fetch and verify external data.

Answer

A state channel to communicate with weather APIs directly.

Answer

An inter-blockchain communication protocol to query a weather-focused sidechain.

Answer

A hard-fork of the main blockchain to include a weather data feed.

Question 2

A developer deploys a complex dApp to the Ethereum network. Users report that their transactions are failing or taking a very long time to confirm during periods of high network activity. The developer advises users to increase the 'gas price' in their wallet settings. What is the primary function of 'gas' in this context?

Accepted Answer

It is a unit measuring the computational effort required for a transaction, which validators are compensated for.

Answer

It is a unit used to measure the dApp's on-chain storage requirements.

Answer

It is a fixed fee paid to the dApp developers for using their service.

Answer

It is a mechanism for funding the Ethereum Foundation's research and development.

Question 3

A development team is building a decentralized social media platform. They want to ensure the user interface is fast and responsive, similar to a traditional web app, while the core logic for content ownership and user interactions is handled by smart contracts. Which of the following BEST describes a typical architectural stack for such a dApp?

Accepted Answer

A traditional frontend (HTML/CSS/JS) interacts with smart contracts for backend logic, and may use decentralized storage (like IPFS) for media files.

Answer

The entire application, including the frontend UI and all data, is stored and executed directly on the blockchain.

Answer

The application logic is run on a centralized server which then batches transactions and submits them to the blockchain.

Answer

Smart contracts are used to query a centralized database where all user data and application logic is stored.

Question 4

A DeFi protocol's smart contract contains a function that sends funds to an external address. An attacker discovers that they can repeatedly call this function from their own malicious contract before the original function completes its state update, allowing them to withdraw more funds than they are entitled to. This vulnerability is known as a:

Accepted Answer

Reentrancy Attack

Answer

Integer Overflow Attack

Answer

Timestamp Dependence Vulnerability

Answer

Front-Running Attack

Question 5

Due to the immutable nature of blockchains, fixing a bug in a deployed smart contract is a significant challenge. Which design pattern allows developers to update the application logic of a dApp without requiring users to migrate their data to a new contract address?

Accepted Answer

The Proxy Pattern

Answer

The Singleton Pattern

Answer

The Factory Pattern

Answer

The Observer Pattern

Question 6

Which of the following describes a Decentralized Autonomous Organization (DAO)?

Accepted Answer

An internet-native organization where rules are encoded as smart contracts and operational decisions are made by its members, typically through voting with governance tokens.

Answer

A corporation that uses blockchain to track its physical assets and supply chain.

Answer

A government agency that uses smart contracts to automate regulatory compliance.

Answer

A software company that develops dApps for a variety of blockchain platforms.