On back, big black patch diagnosis is -

Ans. is 'b' i.e., Becker nevus Becker Nevuso Usually starts in adolescence as an irregular smooth hyperpigmented macule.o Usually involves shoulder, anterior chest and scapular region, although any part of the may be involved,o Slowly grows in size of a palm wile acquiring thick dark hair,o Often lesion resembling acne vulgaris in different stages may appear on surface,o No treatment is required.Seborrheic melanosiso Brownish black pigmentation typically distributrd over seborrhea areas (forehead & beard, retro auricular folds, neck, upper part of chest, interscapular areas) accompanied by erythema and itching.Lichen planus pigmentosuso Hyperpigmented dark brown or slate grey macules distributed mainly over exposed areas and flexures.Pityriasis versicoloro Dark brown to black overlapping confluent patches with satellite lesions, mainly over upper trunk and extending to upper arms, neck and abdomen.