The major product formed in the following reaction is

The reaction medium is strongly acidic and generates the electrophile $$NO_2^+$$ (nitronium ion) in situ.

Anisole contains a lone-pair bearing $$-OCH_3$$ group. Through resonance this group donates electron density to the ring and activates it toward electrophilic substitution. The resonance structures place the highest electron density at the ortho (2, 6) and para (4) positions.

Because of this activation:
$$\text{anisole} + NO_2^+ \;\longrightarrow\; \text{ortho/para-nitroanisoles}$$

Steric hindrance next to the bulky methoxy group disfavors attack at the two ortho positions, whereas the para site is sterically unhindered. Hence the para product dominates.

Therefore the major product is para-nitroanisole, shown in Option B.

Option B which is: $$\mathbf{4\text{-}nitroanisole}$$