Question:medium

The radioisotope, tritium 13(H) has a half-life of 12.3 years. If the initial amount of tritium is 32 mg, how many milligrams of it would remain after 49.2 years:

Updated On: Apr 27, 2026
  • 1 mg

  • 2 mg

  • 4 mg

  • 8 mg

Show Solution

The Correct Option is B

Solution and Explanation

To determine how much tritium remains after 49.2 years, we need to use the concept of radioactive decay and half-life. The half-life of tritium \((^3_1H)\) is the time required for half of the radioactive nuclei to decay.

The formula to calculate the remaining amount of a radioisotope after a certain period is given by:

N = N_0 \left(\frac{1}{2}\right)^{\frac{t}{t_{1/2}}}

where:

  • N = remaining amount of the isotope
  • N_0 = initial amount of the isotope (32 mg in this case)
  • t = time elapsed (49.2 years)
  • t_{1/2} = half-life of the isotope (12.3 years)

Substituting the given values into the formula, we have:

N = 32 \left(\frac{1}{2}\right)^{\frac{49.2}{12.3}}

Calculate the exponent:

\frac{49.2}{12.3} = 4

Thus, the formula becomes:

N = 32 \left(\frac{1}{2}\right)^{4}

Calculate the power of the half:

N = 32 \times \frac{1}{16}

Therefore, N = 2 \, \text{mg}.

After 49.2 years, 2 mg of the initial 32 mg of tritium will remain.

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