Step 1: Understanding the Bohr radius.
The Bohr radius \( a_0 \) is the radius of the smallest orbit around the nucleus in a hydrogen atom. It is given by the formula:
\[
a_0 = \frac{4 \pi \epsilon_0 h^2}{m_e e^2}
\]
where:
- \( \epsilon_0 \) is the permittivity of free space,
- \( h \) is Planck’s constant,
- \( m_e \) is the electron mass,
- \( e \) is the electron charge.
Step 2: Numerical value.
The numerical value for the Bohr radius is approximately \( 0.53 \, \text{Å} \).
Step 3: Conclusion.
Thus, the Bohr radius of a hydrogen atom is \( a_0 \approx 0.53 \, \text{Å} \).