Which among the following relations is/are valid ONLY for reversible process undergone by a pure substance?

The first law of thermodynamics takes the form $$W = - \Delta \,H$$ when applied to :

Round the clock cooling of an apartment having a load of $$300$$ $$MJ/day$$ requires and air-conditioning plant of capacity about

A body of weight $$100$$ $$N$$ falls freely a vertical distance of $$50m$$.The atmospheric drag force is $$0.5N.$$ For the body, the work interaction is