A radioactive sample at some instant has a disintegration rate of $5000$ disintegrations per minute. After $5$ minutes, the rate becomes $1250$ disintegrations per minute. Then, the decay constant (per minute) is

• Correct answer
  A

  $\text{0.4}\text{ ln }2$
• B

  $\text{0.2}\text{ ln }2$
• C

  $\text{0.1}\text{ ln }2$
• D

  $\text{0.8}\text{ ln }2$

Hence, the correct answer is option: 'A'.