The fundamental radio antenna is a metal rod which has a length equal to

• A

  $\lambda$ in free space at the frequency of operation
• B

  $\frac{\lambda}{2}$ in free space at the frequency of operation
• Correct answer
  C

  $\frac{\lambda}{4}$ in free space at the frequency of operation
• D

  $\frac{3 \lambda}{4}$ in free space at the frequency of operation

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