The density of air is `0.001293g//ml` at S.T.P. Its vapour density will be:

Options

A. 10
B. 15
C. 1.468
D. 14.68

Answer

To find the vapor density of air given its density at STP, we can follow these steps:

### Step 1: Understand the relationship between density and molecular weight
The vapor density (VD) of a gas is defined as half of its molecular weight (MW). Therefore, we can express this relationship as:
\[ \text{VD} = \frac{\text{MW}}{2} \]

### Step 2: Use the ideal gas law to find the molecular weight
At STP (Standard Temperature and Pressure), one mole of any gas occupies a volume of 22.4 liters, which is equivalent to 22,400 mL.

### Step 3: Calculate the mass of one mole of air using its density
Given the density of air is \(0.001293 \, \text{g/mL}\), we can calculate the mass of one mole of air:
\[ \text{Mass} = \text{Density} \times \text{Volume} \]
\[ \text{Mass} = 0.001293 \, \text{g/mL} \times 22400 \, \text{mL} \]
\[ \text{Mass} = 29.0 \, \text{g} \]

### Step 4: Find the molecular weight of air
Now that we have the mass of one mole of air, we can say that the molecular weight (MW) of air is:
\[ \text{MW} = 29.0 \, \text{g/mol} \]

### Step 5: Calculate the vapor density
Using the relationship between vapor density and molecular weight:
\[ \text{VD} = \frac{\text{MW}}{2} \]
\[ \text{VD} = \frac{29.0 \, \text{g/mol}}{2} \]
\[ \text{VD} = 14.5 \]

### Conclusion
The vapor density of air is approximately \(14.5\).

---