Question

The active mass of $64$ gm of HI in a two litre flask would be:

• A. $2$
• B. $1$
• C. $5$
• D. $0.25$

Answer 1

The correct option is D

$0.25$

The explanation for the correct option:

Option(C):

Step 1: Expression for the active mass :

Active mass is given by:

$$\begin{gathered} =\frac{(\mathrm{number}\mathrm{of}\mathrm{moles})}{(\mathrm{volume}\mathrm{in}\mathrm{litres})} \\ =\frac{\left({\displaystyle \frac{\mathrm{mass}}{\mathrm{molar}\mathrm{mass}}}\right)}{(\mathrm{volume}\mathrm{in}\mathrm{litres})} \end{gathered}$$

We know,

$$\begin{gathered} \mathrm{H}=1\mathrm{g}/\mathrm{mol} \\ \mathrm{I}=127\mathrm{g}/\mathrm{mol} \end{gathered}$$

Step 2: Calculation of active mass:

On substituting the values, we get,

Active mass = $(64/128)/2$

Active mass = $(0.5)/2$

Active mass =$0.25$

Hence, the active mass of $64$ gm of $\mathrm{HI}$ in a two-liter flask is $0.25$