Question

A certain radioactive isotope ${}_Z^A\text{X}$ (half-life =10 days) decays to give ${}_{Z-2}^{A-4}\text{X}$ . If 1.0 g of X is kept in a sealed vessel. Find the volume of He accumulated at STP in 20 days.

[Molar mass of ${}_Z^A\text{X}=253u$]

• A. 22.40 mL
• B. 33.40 mL
• C. 55.40 mL
• D. 66.40 mL

Answer 1

The correct option is D 66.40 mL

Mass of $X$ decay = 0.75 g

Moles of $X$ decayed $=\frac{0.75}{253}=$ moles of $He$ formed.

Volume (mL) of $He$ at STP $=\frac{0.75\times 22400}{253}$

$=66.40ml$

Hence, option D is correct.