Final answer:
To make a decimal number a whole number, multiply it by 100.
Step-by-step explanation:
To make a decimal number a whole number, you need to multiply it by a factor that will eliminate the decimal part. In this case, the question asks for 10.5 times a decimal number to become a whole number. The correct option is Option C: Multiply by 100. When you multiply a decimal number by 100, you are essentially moving the decimal point two places to the right, which eliminates the decimal part.