Frequently asked: Blockchain Interview Questions and Answers

Q1. What is Blockchain?

Blockchain is a system of recording information in a way that makes it difficult or impossible to change, hack, or cheat the system. A blockchain is essentially a digital ledger of transactions that is duplicated and distributed across the entire network of computer systems on the blockchain. Each block in the chain contains a number of transactions, and every time a new transaction occurs on the blockchain, a record of that transaction is added to every participant’s ledger.

Q2. What are block records?

A block records some or all of the most recent transactions not yet validated by the network. Once the data are validated, the block is closed. Then, a new block is created for new transactions to be entered into and validated.

Q3. What is a Genesis Block?

In 2009, a developer named Santoshi Nakamoto created the genesis block. The genesis block is the first block in the blockchain and is also referred to as block 0. Some features of this block are as follows:

• It is the only block that does not refer to any previous block.

• It defines parameters of blockchain such as level of difficulty, consensus mechanism, etc. to mine the blocks.

The genesis block forms the foundation of the Bitcoin trading system, and it is the prototype for all other blocks in the blockchain.

Q4. Is it possible to modify the data written in the block?

No, it is not possible to modify the data in one particular block. If the need arises, the organization has to erase data from all the other blocks. Due to this reason, it is very important to deal with data with utmost care in the blockchain.

Q5. What is the difference between public and private keys?

Public Keys:

• It is used for identification.

• The sender can send a message in the blockchain network using the public key of the receiver.

• It is free to use and publicly available.

Private Keys:

• It is used for encryption and authentication purposes.

• The receiver can decrypt the message the received message in the blockchain network using the private key.

• It is kept secret and is not available publicly.

Q6. What is a 51% Attack?

A miner or a group of miners attempting to control more than 50% of a network’s hashing capacity, processing power, or hash rate is known as a 51 percent attack on a blockchain network. The attacker may prevent new transactions from taking place or being verified in this attack. They can also reverse transactions that have already been verified while in charge of the network, resulting in a double-spending problem.

Q7. What is Merkel Tree?

Merkel Tree is a data structure that is used for verifying a block. It is in the form of a binary tree containing cryptographic hashes of each block. A Merkle tree is structured similarly to a binary tree where each leaf node is a hash of a block of transactional data and each non-leaf node is a hash of its leaf node. The Merkel root or hash root is the final hash root of all the transaction hashes. It encompasses all the transactions that are underlying all the non-leaf nodes.

Q8. What are smart contracts on blockchain?

Smart contracts are simply programs stored on a blockchain that run when predetermined conditions are met. They typically are used to automate the execution of an agreement so that all participants can be immediately certain of the outcome, without any intermediary’s involvement or time loss.

Q9. What are ADA smart contracts?

A smart contract is an automated digital agreement, written in code, that tracks, verifies, and executes the binding transactions of a contract between various parties. The transactions of the contract are automatically executed by the smart contract code when predetermined conditions are met.

Q10. What is solidity in blockchain?

Solidity is an object-oriented programming language for writing smart contracts. It is used for implementing smart contracts on various blockchain platforms, most notably, Ethereum.

Q11. Can anyone remove blocks from a Blockchain?

The manner in which blocks are removed from a blockchain is entirely dependent on how they are treated. Manually removing a block is not possible. If it is destroyed, however, the blockchain may attempt to restore the database using other peers. They can be removed after they’ve been checked to reduce the blockchain’s size since they don’t need someone to perform regular operations. It can be re-downloaded if necessary. This process is called pruning.

Q12. List and explain the parts of EVM Memory.

The EVM memory can be divided into three parts:

Storage: It is extremely expensive and the storage values are stored permanently on the blockchain network.

Memory: It is temporary modifiable storage that can be accessed only during the contract execution. Once the contract execution is finished, all the data is lost.

  • Stack: It is temporary non-modifiable storage and the content is lost once the execution completes.

Q13. What is a Dapp and how is it different from a normal application?


• A Dapp is a decentralized application that is deployed using a smart contract

• A Dapp has its back-end code (smart contract) which runs on a decentralized peer-to-peer network

• Process: Front-end, Smart contract (backend code), and Blockchain (P2P contract)

Normal application:

• Normal application has a back-end code that runs on a centralized server

• It’s a computer software application that is hosted on a central server

• Process: Front-end, API, and Database

Q14. What is MetaMask?

MetaMask is a type of Ethereum wallet that bridges the gap between the user interfaces for Ethereum (For Example, Mist browsers, DApps, etc.) and the regular web (For Example, Google Chrome, Mozilla Firefox, Websites, etc.). Its function is to inject a JavaScript library called web3.js into the namespace of each page the browser loads. It is mainly used as a plugin in the regular web (For Example, Google Chrome, Mozilla Firefox, etc.)

Q15. How can you stop double-spending?

Double spending is prevented using the consensus algorithm. The consensus algorithm ensures that the requested transaction is genuine and records it in the block. It is thus verified by the multiple nodes thus making double-spending not possible.

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