A record that cannot be altered

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. A record has just been added to a blockchain. Can someone go back and edit it?

A Yes, the owner can edit it at any time

B No, it cannot be changed once added

2. A user wants to remove an old transaction from the blockchain. What happens?

A It cannot be deleted and stays in the history

B It is deleted after the user asks the network

3. A payment was recorded with the wrong amount. How is the mistake fixed?

A The old record is edited to the right amount

B A new record is added to correct it

4. Which word describes a blockchain record that cannot be changed or deleted?

A Immutable

B Editable

5. What happens to the history of transactions on a blockchain over time?

A It stays permanent and fixed

B Old parts are erased to save space

Match the Pairs

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

Left column		Right column
1immutable		AA mistake is fixed by adding a new record, not by editing the old one
2add_record(correction)		BRecords on a blockchain cannot be edited, so you cannot change the amount of an old record. Add a new correcting record instead.
3Old records cannot be edited, so trying to change a past amount is refused		Cdelete(block5) -> REFUSED
4Old records cannot be deleted, so the history stays permanent		DA record that cannot be changed or deleted once it has been added to the blockchain
5change_amount(old_record, 50)		ERecords on a blockchain cannot be deleted, so you cannot erase a mistake. Add a new record that corrects it instead.
6remove(old_record)		Fedit(block5, amount) -> REFUSED

Definitions

immutable

Fill in the Blanks

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

blockchain.______(record)

correction ← NewRecord(-50) blockchain.append(__________)

immutable ← ____

IF record.immutable = TRUE THEN ______ "Cannot edit"

history ← history _ newRecord

Spot the Error

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

Question 1

A chain ← []

B ADD(chain, 'A pays B 5')

C ADD(chain, 'B pays C 2')

D chain[2] ← 'B pays C 3'

E OUTPUT LENGTH(chain)

Question 2

A chain ← []

B ADD(chain, 'A pays B 5')

C DELETE(chain, 1)

D OUTPUT chain

Question 3

A record ← 'A pays B 5'

B locked ← TRUE

C IF locked = TRUE THEN

D record ← 'A pays B 50'

E ENDIF

Question 4

A immutable ← FALSE

B IF immutable = TRUE THEN

C OUTPUT 'Record is fixed'

D ENDIF

Question 5

A chain ← ['A pays B 5']

B chain ← ['B pays C 2']

C OUTPUT LENGTH(chain)

D OUTPUT chain[1]

Answer Key

A record that cannot be altered

Section A: Quick Questions

B — No, it cannot be changed once added

A — It cannot be deleted and stays in the history

B — A new record is added to correct it

A — Immutable

A — It stays permanent and fixed

Section B: Match the Pairs

immutable → A record that cannot be changed or deleted once it has been added to the blockchain

add_record(correction) → A mistake is fixed by adding a new record, not by editing the old one

Old records cannot be edited, so trying to change a past amount is refused → edit(block5, amount) -> REFUSED

Old records cannot be deleted, so the history stays permanent → delete(block5) -> REFUSED

change_amount(old_record, 50) → Records on a blockchain cannot be edited, so you cannot change the amount of an old record. Add a new correcting record instead.

remove(old_record) → Records on a blockchain cannot be deleted, so you cannot erase a mistake. Add a new record that corrects it instead.

Section C: Definitions

immutable — Cannot be changed or deleted once added. A blockchain record stays fixed, so mistakes are fixed by adding a new record and the history stays permanent.

Section D: Fill in the Blanks

blockchain.append(record)

correction ← NewRecord(-50)
blockchain.append(correction)

immutable ← TRUE

IF record.immutable = TRUE THEN
    OUTPUT "Cannot edit"

history ← history + newRecord

Section E: Spot the Error

D — An old record on a blockchain cannot be edited. The mistake must be fixed by adding a new correction record with ADD, not by overwriting chain[2].

C — Old records cannot be deleted from a blockchain. The mistake is fixed by adding a new correction record, so line 3 should be ADD(chain, 'Fix: A pays B 4').

D — When a record is locked it cannot be altered. The program should refuse the edit with a message, not change the record's value.

A — Blockchain records are immutable, which means they cannot be changed. The variable should be set to TRUE, not FALSE.

B — This replaces the whole chain and erases the first record. History must stay permanent, so the new record should be added with ADD(chain, 'B pays C 2').