The magnitude of the first ionization energy for Na  is equal to :

The electronic configuration we have,

$\mathrm{Na}-\left[\mathrm{Ne}\right]3{\mathrm{s}}^1$

Sodium has one valence electron in the state and achieves a stable configuration by losing this electron. Thus, The magnitude of the first ionization energy for Na is equal to the energy of its$3{\mathrm{s}}^1$electron. 

Hence, the correct option is A.