MCQ practice · SSC Chemistry Board questions · Chapter 6: Concept of Mole and Chemical Counting
How many molecules are there in 1 g of the salt KCl?
Think it through first, then pick an option.
- a 8.084 × 10²¹
- b 8.084 × 10²²
- c 8.084 × 10²³
- d 8.084 × 10²⁴
Answer and explanation
Correct answer: a 8.084 × 10²¹
KCl = 39 + 35.5 = 74.5; molecules in 1 g = 6.023 × 10²³/74.5 = 8.084 × 10²¹.
Why the other options are wrong
- b 8.084 × 10²²: 8.084 × 10²² is the count in 10 g of KCl; 1 g holds 8.084 × 10²¹.
- c 8.084 × 10²³: 8.084 × 10²³ is more than a mole, the count in 100 g; 1 g holds 8.084 × 10²¹.
- d 8.084 × 10²⁴: 8.084 × 10²⁴ is the count in 1000 g; 1 g holds 8.084 × 10²¹.
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