Question

Which one of the following gases contains the least number of molecules?

[Atomic weight of $P=31,Cl=35.5,N=14,O=16,C=12,H=1$]

• A. $4.0$ g of Laughing gas
• B. $3.0$ g of Phosphine
• C. $2.0$ g of Marsh gas
• D. $10.0$ g of Phosgene

Answer 1

The correct option is B $3.0$ g of Phosphine

Mole is the SI unit of measurement used to measure the number of things, usually atoms or molecules. One mole of something is equal to $6.02214078\times {10}^{23}$ of same things particles (Avogadro's number).

4.0 g of Laughing gas $\left(N_{2}O\right)$ contain $\frac{4}{44}\times 6.022\times {10}^{23}=0.0909\times 6.023\times {10}^{23}$ molecules

3.0 g of phosphine $\left(P{H}_3\right)$ contain $\frac{3}{34}\times 6.022\times {10}^{23}=0.088\times 6.023\times {10}^{23}$ molecules

2.0 g of Marsh gas $\left(C{H}_4\right)$ contain $\frac{2}{16}\times 6.022\times {10}^{23}=0.125\times 6.023\times {10}^{23}$ molecules

10 g of Phosgene $\left(COC{l}_2\right)$ contain $\frac{10}{99}\times 6.022\times {10}^{23}=0.1010\times 6.023\times {10}^{23}$ molecules

So 3.0 gram of phosphine gas contain least number of molecules.