Question

Number of moles is 128 gm of sulphur($S_8$) will be:

• A. 0.5
• B. 2
• C. 4
• D. 8

Answer 1

The correct option is A 0.5

$\text{Number of moles}=\frac{\text{Weight of compound}}{\text{Molar mass of compound}}$
The sulphur molecule exists as $S_8$ molecule. Its molar mass is $8\times 32g/mol=256g/mol$.
128 g of sulphur corresponds to $\frac{128g}{256g/mol}=0.5mol$.