Identify '$$\mathrm{A}$$' in the following reaction.

A+ Acetic anhydride $$\xrightarrow{\mathrm{H}^{+}}$$ Aspirin + Acetic acid

What is the value of $$\angle \mathrm{S}-\mathrm{S}-\mathrm{S}$$ in puckered $$\mathrm{S}_8$$ rhombic sulfur?

Identify the reagent used in the following reaction.

Benzoic acid $$\xrightarrow[\Delta]{\text { Reagent }}$$ Benzoyl chloride + Phosphorous oxychloride + Hydrogen chloride

Which activity from following is exhibited by Lewis base according to definition?