Top 75+ Blockchain Interview Questions and Answers (2025 Updated)

Blockchain Overview

Blockchain is a decentralized, distributed digital ledger technology that records transactions across a network of computers in a secure, transparent, and tamper-proof way. It enables the transfer of data or assets without the need for a central authority.

Key Features of Blockchain

1. Decentralization: No central authority—data is shared across all participants (nodes).

2. Immutability: Once recorded, transactions cannot be altered or deleted.

3. Transparency: Every participant can view the ledger and verify transactions.

4. Security: Advanced cryptography ensures data integrity and authenticity.

5. Consensus Mechanisms: Nodes agree on the validity of transactions using methods like Proof of Work (PoW) or Proof of Stake (PoS).

How Blockchain Works (Simplified):

1. A transaction is requested.

2. The transaction is broadcast to a peer-to-peer network.

3. The network validates the transaction using a consensus algorithm.

4. Once validated, the transaction is added to a block.

5. The new block is added to the existing blockchain (ledger).

6. The transaction is complete and permanently recorded.

Types of Blockchains:

• Public Blockchain: Open to anyone (e.g., Bitcoin, Ethereum).

• Private Blockchain: Restricted access, used by organizations.

• Consortium Blockchain: Controlled by a group of organizations.

Common Applications:

• Cryptocurrencies: Like Bitcoin and Ethereum.

• Smart Contracts: Self-executing contracts with the terms directly written in code.

• Supply Chain: End-to-end tracking of goods.

• Healthcare: Secure patient data sharing.

• Voting Systems: Transparent and tamper-resistant elections.

Blockchain Interview Questions:

1 .What is Blockchain?

A Blockchain is a constantly growing ledger(file) that keeps a permanent record of all the transactions that have taken place, in a secure, chronological, and immutable way. It can be used for the secure transfer of money, property, contracts, etc. without requiring a third-party intermediary like bank or government.
 
Blockchain is the backbone of the most famous cryptocurrency named Bitcoin. It is a peer to peer electronic cash system and a decentralized network which allows users to make transactions directly without the involvement of third-party to manage the exchange of funds.

Let's breakdown the definition :
 
Ledger : It is a file that is constantly growing.

Permanent : It means once the transaction goes inside a blockchain, you can put up it permanently in the ledger.

Secure : Blockchain placed information in a secure way. It uses very advanced cryptography to make sure that the information is locked inside the blockchain.

Chronological : Chronological means every transaction happens after the previous one.

Immutable : It means as you build all the transaction onto the blockchain, this ledger can never be changed.

A blockchain is a chain of blocks which contain information. Each block records all of the recent transactions, and once completed goes into the blockchain as a permanent database. Each time a block gets completed, a new block is generated..

2 .What are 'blocks' in Blockchain?

A Blockchain comprises of many blocks consisting of financial transaction information. Each block has a timestamp, the transaction data, and a unique hash pointer that acts as a link between it and the block immediately before it. Together, all blocks combine to form a Blockchain.

3 .What is Blockchain 'encryption'?

Blockchain assures a safe and secure ecosystem for data, and that it does through encryption. Essentially, encryption is the process where data is encoded or altered slightly before a user sends it out of a network. This ensures data safety and security since only the sender and receiver know the key to decode the encrypted code.

4 .What are the two types of records present in a Blockchain database?

A Blockchain database has two types of records :
 
Both of these records are easily accessible, and they can even be integrated with each other.

5 .What are the key features of Blockchain?

The central characteristics of Blockchain are :
 

6 .Why is Blockchain a trusted approach?

* Blockchain can be trusted due to so many reasons.

* Its compatibility with other business applications due to its open-source nature.

* Its security. As it was meant for online transactions, the developers have paid special attention to keeping up the pace when it comes to its security.

* It really doesn’t matter what type of business one owns, Blockchain can easily be considered.

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