Rollups (Optimistic vs ZK) in Blockchain / Solidity - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Optimistic Rollup Fraud Proof Simulation

Consider the following simplified Python code simulating an optimistic rollup fraud proof check. What is the output when the code runs?

Blockchain / Solidity

def optimistic_rollup_check(state, new_state):
    # Fraud proof triggers if new_state is less than state
    if new_state < state:
        return "Fraud detected"
    else:
        return "State accepted"

print(optimistic_rollup_check(100, 90))

A State accepted

B Fraud detected

C TypeError

D SyntaxError

💡 Hint

Think about the condition that triggers fraud detection in optimistic rollups.

The function checks if the new state is less than the current state. Since 90 < 100, it returns 'Fraud detected'.

🧠 Conceptual

intermediate

Difference in Verification Time Between Rollups

Which statement correctly describes the verification time difference between Optimistic Rollups and ZK Rollups?

A Optimistic Rollups use zero-knowledge proofs for instant verification

B Optimistic Rollups verify transactions instantly, ZK Rollups delay verification

C Both rollups verify transactions instantly with no delay

D ZK Rollups verify transactions instantly using proofs, Optimistic Rollups delay verification due to fraud proofs

💡 Hint

Recall how each rollup type handles transaction verification.

ZK Rollups generate cryptographic proofs that verify transactions instantly, while Optimistic Rollups assume transactions are valid and only verify if a fraud proof is submitted, causing delay.

🔧 Debug

advanced

Identify the Error in ZK Rollup Proof Generation Code

What error will the following Python code raise when simulating a ZK Rollup proof generation?

Blockchain / Solidity

def generate_zk_proof(data):
    # Simulate proof generation
    proof = data / 0
    return proof

print(generate_zk_proof(10))

A ZeroDivisionError

B No error, outputs 0

C ValueError

D TypeError

💡 Hint

Look at the operation dividing by zero.

Dividing any number by zero in Python raises a ZeroDivisionError.

📝 Syntax

advanced

Syntax Error in Optimistic Rollup Challenge Period Code

Which option contains the correct syntax to define a function that returns the challenge period length in days?

Blockchain / Solidity

def challenge_period():
    return 7

A

def challenge_period()
    return 7

B

def challenge_period():
return 7

C

def challenge_period():
    return 7

D

def challenge_period:
    return 7

💡 Hint

Check for colons and indentation in function definitions.

Option C correctly includes the colon after the function name and indents the return statement properly.

🚀 Application

expert

Calculate Final State After Batch Processing in ZK Rollup

Given the following Python code simulating batch state updates in a ZK Rollup, what is the final state printed?

Blockchain / Solidity

def zk_rollup_batch(states):
    final_state = 0
    for s in states:
        final_state += s * 2
    return final_state

batch_states = [1, 3, 5]
print(zk_rollup_batch(batch_states))

A 18

B 9

C 15

D 30

💡 Hint

Multiply each state by 2 and add them all up.

The function doubles each state and sums them: (1*2)+(3*2)+(5*2) = 2+6+10 = 18.