The reaction of methoxybenzene with nitronium ion will result 1-methoxy-4-nitrobenzene. The methoxy group is considered electron donating group, and it will push the electron toward the aromatic ring. So, it works on stabilizing the compound at para position more than meta position. This is because of resonance donating effect that increases the electron density at para position rather than meta position. The resonance at para position gives carbocation on two secondary carbons and one tertiary carbon. The electron donating group will push the electrons toward the positive charge on tertiary carbon, so it makes the ring stable. This leads the nitronium ion to attach at para position.

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