Question

Ba-122 has half-life of 2 min. Experiment has to be done using Ba-122 and it takes 10 min to set up the experiment. It initially had 80 g of Ba-122. How much Ba-122 was left when the experiment started?

• A. 2.5 g
• B. 5 g
• C. 10 g
• D. 20 g

Hint:

Use the formula \( m = m_0 \cdot \left( \frac{1}{2} \right)^n \) for radioactive decay after \( n \) half-lives.

Answer 1

The Correct Option is A

Given: - Initial mass = 80 g
- Half-life \( t_{1/2} = 2 \) min
- Time elapsed = 10 min
- Number of half-lives = \( \frac{10}{2} = 5 \) After \( n \) half-lives: \[ \text{Remaining mass} = \frac{80}{2^5} = \frac{80}{32} = 2.5 \, \text{g} \]