A duma bulb full of air weighs 22.567 gm at `20^@C` and 755 mm pressure. Full of vapours of a substance at `120^@C` and the same pressure. It weighs 22.8617 gm. The capacity of the bulb is 200 ml. Find out the molecular mass of the substance. [density of air `=0.00129(gm)/(ml)`]

Explanation

To find the molecular mass of the substance using the Duma bulb data, we can follow these steps:

### Step 1: Calculate the mass of air in the Duma bulb
The volume of the Duma bulb is given as 200 ml, and the density of air is given as 0.00129 g/ml.

\[ \text{Mass of air} = \text{Density} \times \text{Volume} = 0.00129 \, \text{g/ml} \times 200 \, \text{ml} = 0.258 \, \text{g} \]
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