Why blockchain exists - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why was blockchain technology created?

Which of the following best explains the main reason blockchain technology was created?

A To replace all existing internet protocols with a new one

B To create a centralized database controlled by a single authority

C To enable secure, transparent, and tamper-proof record keeping without a central authority

D To speed up traditional banking transactions by using faster servers

💡 Hint

Think about what problem blockchain solves related to trust and control.

Blockchain was created to allow multiple parties to share data securely and transparently without needing a trusted middleman. This prevents tampering and fraud.

🧠 Conceptual

intermediate

What problem does blockchain solve in digital transactions?

What key problem in digital transactions does blockchain technology address?

A The risk of double spending and lack of trust between parties

B The need for faster internet connections

C The difficulty of creating user-friendly apps

D The high cost of physical cash handling

💡 Hint

Consider what happens if someone tries to spend the same digital money twice.

Blockchain prevents double spending by recording transactions in a secure, shared ledger that all participants verify, ensuring trust without intermediaries.

❓ Predict Output

advanced

What is the output of this simplified blockchain block validation code?

Consider this Python code that simulates a simple blockchain block validation. What will it print?

Blockchain / Solidity

block = {'index': 1, 'data': 'Hello', 'previous_hash': '0'*64}

import hashlib

def hash_block(block):
    block_string = f"{block['index']}{block['data']}{block['previous_hash']}"
    return hashlib.sha256(block_string.encode()).hexdigest()

block_hash = hash_block(block)

if block_hash.startswith('0000'):
    print('Block is valid')
else:
    print('Block is invalid')

A KeyError

B Block is invalid

C SyntaxError

D Block is valid

💡 Hint

Look at the hash prefix check and what the hash function returns.

The hash of the block is very unlikely to start with '0000' without special mining. So the code prints 'Block is invalid'.

❓ Predict Output

advanced

What is the output of this blockchain transaction verification code?

What will this JavaScript code print when run?

Blockchain / Solidity

const transactions = [{from: 'Alice', to: 'Bob', amount: 50}, {from: 'Bob', to: 'Charlie', amount: 30}];

function verifyTransaction(tx) {
  return tx.amount > 0 && tx.from !== tx.to;
}

const results = transactions.map(verifyTransaction);
console.log(results);

A [true, true]

B [true, false]

C [false, true]

D [false, false]

💡 Hint

Check the conditions in verifyTransaction for each transaction.

Both transactions have positive amounts and different sender and receiver, so both return true.

🧠 Conceptual

expert

Why is decentralization important in blockchain?

Which of the following best explains why decentralization is a key feature of blockchain?

A It allows a single company to control all data securely

B It makes the blockchain private and hidden from users

C It speeds up transactions by using one central server

D It removes the need for trust in a single authority by distributing control among many participants

💡 Hint

Think about how decentralization affects trust and control.

Decentralization means no single party controls the data, so participants can trust the system without trusting one authority.