What is the chemical formula of isocrotonic acid?

Isocrotonic acid (also known as quartenylic acid; formally named (Z)-2-butenoic acid) is the cis isomer of crotonic acid. It is an oil, possessing a smell similar to that of brown sugar. It boils at 171.9 °C, concomitant with conversion into crotonic acid. Isomerization is complete when the cis acid is heated to 170–180 °C in a sealed tube.

Rudolph Fittig and Hugo Erdmann showed that the γ-phenyl structural analog of isocrotonic acid forms α-naphthol when dehydrated, an observation that provided useful evidence in understanding the nature of naphthalene.

(Z)-(C6H5)CH=CHCH2COOH → α-naphthol + H2O

hydrosulfuric acid is the acid form of Hydrogen sulfide (a gas). If you dissolve Hydrogen sulfide gas in water, you get H2S(aq) AKA sulfhydric acid.