Consensus mechanisms overview in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the consensus mechanism used in Proof of Work.

Blockchain / Solidity

consensus = "[1]"

Drag options to blanks, or click blank then click option'

AByzantine Fault Tolerance

BProof of Stake

CDelegated Proof

DProof of Work

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing Proof of Work with Proof of Stake

Using Delegated Proof as the main consensus

The consensus mechanism used in Bitcoin and many early blockchains is Proof of Work.

2fill in blank

medium

Complete the code to check if the consensus mechanism is energy efficient.

Blockchain / Solidity

if consensus == "[1]":
    print("Energy efficient")
else:
    print("Not energy efficient")

Drag options to blanks, or click blank then click option'

AProof of Stake

BProof of Work

CProof of Authority

DProof of Capacity

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing Proof of Work as energy efficient

Confusing Proof of Authority with energy efficiency

Proof of Stake is known for being more energy efficient than Proof of Work.

3fill in blank

hard

Fix the error in the code to correctly identify the consensus mechanism that uses voting among nodes.

Blockchain / Solidity

if consensus == "[1]":
    print("Uses voting among nodes")

Drag options to blanks, or click blank then click option'

AProof of Work

BByzantine Fault Tolerance

CProof of Stake

DProof of Capacity

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing it with Proof of Stake

Choosing Proof of Work which is puzzle-based

Byzantine Fault Tolerance consensus involves nodes voting to agree on the next block.

4fill in blank

hard

Fill both blanks to create a dictionary mapping consensus mechanisms to their main characteristic.

Blockchain / Solidity

consensus_info = {
    "Proof of Work": "[1]",
    "Proof of Stake": "[2]"
}

Drag options to blanks, or click blank then click option'

AHigh energy consumption

BLow energy consumption

CFast finality

DDecentralized voting

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up energy consumption characteristics

Using voting or finality terms incorrectly

Proof of Work consumes high energy, while Proof of Stake is low energy.

5fill in blank

hard

Fill both blanks to create a dictionary comprehension filtering consensus mechanisms with energy consumption less than 100.

Blockchain / Solidity

energy_use = {
    "PoW": 1000,
    "PoS": 10,
    "BFT": 50
}
low_energy = {k: v for k, v in energy_use.items() if v {BLANK_2}} {{BLANK_2}}

Drag options to blanks, or click blank then click option'

A:

B<

C100

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '<' in the condition

Forgetting the colon ':' in the comprehension

The dictionary comprehension uses ':' to map keys to values, and filters values less than 100.

Practice

1. Which of the following best describes the main purpose of a consensus mechanism in blockchain?

easy

A. To store large files on the blockchain

B. To speed up internet connections

C. To help multiple computers agree on a single version of data

D. To encrypt messages between users

Solution

1. Step 1: Understand the role of consensus

   Consensus mechanisms ensure all participants agree on the same data state.

2. Step 2: Compare options

   Only To help multiple computers agree on a single version of data describes agreement on data; others describe unrelated functions.

3. Final Answer:

   To help multiple computers agree on a single version of data -> Option C

4. Quick Check:

   Consensus = Agreement [OK]

Hint: Consensus means agreement among many computers [OK]

Common Mistakes:

• Confusing consensus with encryption
• Thinking consensus speeds up internet
• Mixing storage with agreement

2. Which syntax correctly names a popular consensus mechanism used in many blockchains?

easy

A. Proof of Walk

B. Proof of Work

C. Proof of Wait

D. Proof of Watch

Solution

1. Step 1: Recall common consensus names

   Proof of Work is a widely used consensus mechanism name.

2. Step 2: Check spelling and meaning

   Options B, C, and D are incorrect or made-up terms.

3. Final Answer:

   Proof of Work -> Option B

4. Quick Check:

   Correct name = Proof of Work [OK]

Hint: Remember the exact phrase: Proof of Work [OK]

Common Mistakes:

• Misspelling 'Work' as 'Walk' or 'Wait'
• Confusing similar-sounding words
• Assuming all options are valid

3. Consider this simplified pseudocode for a blockchain consensus check:

if node_vote > 50%:
    accept_block = True
else:
    accept_block = False
print(accept_block)

What will be printed if node_vote is 45?

medium

A. False

B. True

C. SyntaxError

D. None

Solution

1. Step 1: Evaluate the condition with node_vote = 45

   45 is not greater than 50%, so condition is False.

2. Step 2: Determine the value of accept_block

   Since condition is False, accept_block is set to False and printed.

3. Final Answer:

   False -> Option A

4. Quick Check:

   45 > 50%? No, so False [OK]

Hint: Check if vote is over 50% to accept block [OK]

Common Mistakes:

• Assuming 45 is greater than 50%
• Confusing True/False outputs
• Expecting syntax errors in simple if-else

4. The following code tries to check if a block is accepted using Proof of Stake but has an error:

stake = 30
if stake >= 50
    block_accepted = True
else:
    block_accepted = False
print(block_accepted)

What is the error?

medium

A. Missing colon after if condition

B. Wrong variable name 'stake'

C. Indentation error on else

D. print statement syntax error

Solution

1. Step 1: Check if statement syntax

   The if statement is missing a colon ':' at the end of the condition line.

2. Step 2: Verify other parts

   Variable names, indentation, and print syntax are correct.

3. Final Answer:

   Missing colon after if condition -> Option A

4. Quick Check:

   if statement needs ':' [OK]

Hint: Always put ':' after if conditions [OK]

Common Mistakes:

• Ignoring missing colon errors
• Thinking indentation is wrong
• Assuming variable names cause error

5. You want to design a blockchain that uses Proof of Stake but only allows nodes with at least 100 tokens to vote. Which code snippet correctly filters nodes before voting?

hard

A. valid_nodes = [node for node in nodes if node.tokens < 100]

B. valid_nodes = [node for node in nodes if node.tokens > 1000]

C. valid_nodes = [node for node in nodes if node.tokens == 50]

D. valid_nodes = [node for node in nodes if node.tokens >= 100]

Solution

1. Step 1: Understand the filtering condition

   Nodes must have at least 100 tokens, meaning tokens >= 100.

2. Step 2: Check each option's condition

   valid_nodes = [node for node in nodes if node.tokens >= 100] uses >= 100, matching requirement; others do not.

3. Final Answer:

   valid_nodes = [node for node in nodes if node.tokens >= 100] -> Option D

4. Quick Check:

   At least 100 tokens = tokens >= 100 [OK]

Hint: Use >= 100 to include nodes with 100 tokens [OK]

Common Mistakes:

• Using > 100 excludes nodes with exactly 100 tokens
• Using < or == filters wrong nodes
• Confusing token count conditions