Blocks joined in a chain

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. Where is a new block added in a blockchain?

A On the end of the chain, after the latest block

B At the start of the chain, before the first block

2. Which statement about how blocks are linked is correct?

A Each new block links to the block before it

B Each new block links only to the next block that has not been made yet

3. In what order are the blocks in a blockchain arranged?

A Alphabetical order of the names of the people sending money

B Time order, from the oldest block to the newest

4. A chain has Block 1, Block 2 and Block 3. Block 4 is made next. What is the new order?

A Block 4, Block 1, Block 2, Block 3

B Block 1, Block 2, Block 3, Block 4

5. You draw a blockchain as a row of boxes. What should join the boxes?

A An arrow or line from each block back to the previous block

B No links, because each block stands on its own

Match the Pairs

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

Left column		Right column
1Block 3 -> Block 2 -> Block 1		ABlock 5: previous = Block 4
2chain = [B1, B2, B3]; chain.append(B4)		BA new block is added to the end of the chain, after the newest existing block
3Blocks are kept in time order, with the oldest block first and the newest block last		CEach block links back to the block before it, so the blocks form a chain
4Each new block stores a link to the block before it		DBlock 1 (09:00) <- Block 2 (09:10) <- Block 3 (09:20)
5New Block 6 is inserted between Block 2 and Block 3		ENew blocks must be added to the end of the chain, not into the middle. Inserting a block breaks the time order of the chain.
6Block 4: previous = none (but Blocks 1 to 3 already exist)		FA block that is not the first one must link to the block before it. Here Block 4 is not linked, so it is not joined to the chain.

Definitions

chain of blocks

Fill in the Blanks

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

Block3.previous ← ______

______ Block4 TO chain

Block5.________ ← Block4

IF Block2.time _ Block1.time THEN OUTPUT "Block 2 is newer" ENDIF

[Block 1]<-[Block 2]<-[Block 3]<-[Block _]

Spot the Error

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

Question 1

A chain = [block1, block2]

B new_block = block3

C chain.insert(0, new_block)

Question 2

A block1.previous = None

B block2.previous = block1

C block3.previous = block2

D block4.previous = block1

Question 3

A block1.time = "09:00"

B block2.time = "09:05"

C block3.time = "08:55"

Question 4

A new ← NewBlock()

B new.previous ← new

C APPEND new TO chain

Question 5

A chain = [block1]

B chain = [block2]

C chain.append(block3)

D print(len(chain))

Answer Key

Blocks joined in a chain

Section A: Quick Questions

A — On the end of the chain, after the latest block

A — Each new block links to the block before it

B — Time order, from the oldest block to the newest

B — Block 1, Block 2, Block 3, Block 4

A — An arrow or line from each block back to the previous block

Section B: Match the Pairs

Block 3 -> Block 2 -> Block 1 → Each block links back to the block before it, so the blocks form a chain

chain = [B1, B2, B3]; chain.append(B4) → A new block is added to the end of the chain, after the newest existing block

Blocks are kept in time order, with the oldest block first and the newest block last → Block 1 (09:00) <- Block 2 (09:10) <- Block 3 (09:20)

Each new block stores a link to the block before it → Block 5: previous = Block 4

New Block 6 is inserted between Block 2 and Block 3 → New blocks must be added to the end of the chain, not into the middle. Inserting a block breaks the time order of the chain.

Block 4: previous = none (but Blocks 1 to 3 already exist) → A block that is not the first one must link to the block before it. Here Block 4 is not linked, so it is not joined to the chain.

Section C: Definitions

chain of blocks — Blocks are added one after another in time order. Each new block goes on the end and links to the block before it, so the blocks form a chain.

Section D: Fill in the Blanks

Block3.previous ← Block2

APPEND Block4 TO chain

Block5.previous ← Block4

IF Block2.time > Block1.time THEN
    OUTPUT "Block 2 is newer"
ENDIF

[Block 1]<-[Block 2]<-[Block 3]<-[Block 4]

Section E: Spot the Error

C — A new block must go on the end of the chain. insert(0, ...) puts it at the start. It should be chain.append(new_block).

D — Each block links to the block directly before it. block4 should link to block3, not skip back to block1: block4.previous = block3.

C — Blocks follow time order. block3 comes after block2 (09:05), so its time must be later, such as 09:10, not 08:55.

B — The new block must link to the last block already in the chain. It cannot link to itself. It should be new.previous ← last_block.

B — This replaces the whole chain, so block1 is lost. A block must be added to the end with chain.append(block2).