Blockchain

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Date:

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Quick Questions

Shade in the A or B circle for each question.

1. Which description matches the basic form of a blockchain in the IGCSE syllabus?

A A digital ledger: a time-stamped series of records that cannot be altered

B A paper notebook kept by one bank that staff can rub out and rewrite

2. What is a ledger?

A A record of transactions

B A type of coin or note

3. Why is a blockchain called a DIGITAL ledger?

A Its records are written by hand on paper

B Its records are stored electronically on computers

4. What does it mean for a blockchain record to be time-stamped?

A The date and time it was made is stored with it

B The record can only be read for a short time

5. How are the records in a blockchain arranged?

A In a random pile with no order

B As a series, one after another in order

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1blockchain		AThe date and time a record was made, stored with that record in the blockchain
2time-stamp		Bcannot be altered
3A blockchain is a ledger that is stored digitally rather than on paper		CA blockchain is a digital ledger, not a paper one, and its records cannot be altered, so they cannot be rubbed out or rewritten.
4Once a record is added to a blockchain, nobody can change it		DA blockchain is a time-stamped series of records kept in order, not a random pile with no time or order.
5A blockchain is a paper ledger that anyone can rub out and rewrite		Edigital ledger
6A blockchain is a random pile of records with no time or order		FA digital ledger: a time-stamped series of records, in order, that cannot be altered

Definitions

blockchain

Fill in the Blanks

Complete each line of code by filling in the missing parts.

Blockchain is a digital ______ of records

Each record has a __________ (date, time)

blockchain ← [R1, R2, R3] FOR EACH r __ blockchain OUTPUT r

canBeAltered ← _____

Records in a blockchain cannot be _______

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A blockchain = 0

B record = {'time': '09:00'}

C blockchain.append(record)

D print(len(blockchain))

Question 2

A ledger = []

B tx = 'Ava pays Liam 5'

C ledger.append(tx)

D ledger[0] = 'Ava pays Liam 50'

Question 3

A chain = []

B now = '2025-01-05 09:00'

C rec = {'time': now, 'amt': 5}

D chain.insert(0, rec)

Question 4

A stamp = 2025-03-01 10:30

B amount = 20

C record = [stamp, amount]

D chain = [record]

Question 5

A chain = ['A>B 5', 'B>C 2']

B chain.append('C>D 1')

C print(chain[3])

D print(len(chain))

Answer Key

Blockchain

Section A: Quick Questions

A — A digital ledger: a time-stamped series of records that cannot be altered

A — A record of transactions

B — Its records are stored electronically on computers

A — The date and time it was made is stored with it

B — As a series, one after another in order

Section B: Match the Pairs

blockchain → A digital ledger: a time-stamped series of records, in order, that cannot be altered

time-stamp → The date and time a record was made, stored with that record in the blockchain

A blockchain is a ledger that is stored digitally rather than on paper → digital ledger

Once a record is added to a blockchain, nobody can change it → cannot be altered

A blockchain is a paper ledger that anyone can rub out and rewrite → A blockchain is a digital ledger, not a paper one, and its records cannot be altered, so they cannot be rubbed out or rewritten.

A blockchain is a random pile of records with no time or order → A blockchain is a time-stamped series of records kept in order, not a random pile with no time or order.

Section C: Definitions

blockchain — A digital ledger: a time-stamped series of records, in order, that cannot be altered.

Section D: Fill in the Blanks

Blockchain is a digital ledger of records

Each record has a time-stamp (date, time)

blockchain ← [R1, R2, R3]
FOR EACH r IN blockchain
    OUTPUT r

canBeAltered ← FALSE

Records in a blockchain cannot be altered

Section E: Spot the Error

A — A blockchain is a series of records, so it must be a list that can hold many records. A single number cannot. Line 1 should be blockchain = [].

D — Records in a blockchain cannot be altered once they are written. This line changes record 0. It should only read the record, as in print(ledger[0]).

D — The records are kept in order, so a new record goes on the end. insert(0, rec) puts it at the start and breaks the order. It should be chain.append(rec).

A — The time-stamp is the date and time of the record, stored as text. Without quotes this is not valid code. It should be stamp = '2025-03-01 10:30'.

C — The chain has 3 records in order, numbered 0, 1 and 2. The newest record is chain[2]. chain[3] does not exist and would cause an error.