The question is asking, "Which number is a multiple of 4?" with the options given as 21, 22, 23, and 24.

To identify a multiple of 4:

• A number is a multiple of 4 if it can be evenly divided by 4 (i.e., the remainder is 0).

Step-by-step check:

1. $21 \div 4 = 5.25$ (Not a multiple)
2. $22 \div 4 = 5.5$ (Not a multiple)
3. $23 \div 4 = 5.75$ (Not a multiple)
4. $24 \div 4 = 6$ (Multiple of 4)

Answer: The number 24 is a multiple of 4.

Would you like further details or have any questions?

Here are five related questions to expand understanding:

1. How do you determine if a number is a multiple of another number?
2. Can a negative number be a multiple of 4? Why?
3. What are the first 10 multiples of 4?
4. How can divisibility rules help identify multiples of 4 quickly?
5. What are some practical applications of finding multiples in real-world scenarios?

Tip: To check if a number is a multiple of 4 quickly, ensure its last two digits form a number divisible by 4.