The mixed ether (P) upon heating with conc. HI undergoes cleavage to form two different alkyl iodides.
Treatment with aq. NaOH converts these iodides to alcohols (Q) and (R).
Both (Q) and (R) giving yellow precipitate with NaOI indicates both are secondary or primary alcohols capable of iodoform reaction.
For both cleavage products to yield iodoform-positive alcohols, the mixed ether must have both alkyl groups capable of forming such alcohols.
Option (1) represents a symmetric mixed ether where both fragments upon HI cleavage yield alcohol products with methyl groups adjacent to OH (secondary alcohols) or methyl ketones after oxidation, both giving positive iodoform test.