Study the given heating curve of substance `X` carefully and select the correct statement.

Options

A. Substance `X` exists in solid state at point `1`, in liquid state at point `3` and in gaseous state at point `5`.
B. `QR` represents latent heat of fusion, while `ST` represents latent heat of vaporisation
C. At `QR`, matter exists both in solid and liquid states, while at `ST` matter exists both in liquid and gaseous states.
D. All of these

Answer

D

Explanation

Below 273 K (PQ), X exists in solid state. At 273 K (QR), interconversion of solid to liquid takes place. Above 273 K (RS), X exists in liquid state. At 373 K (ST). interconversion of liquid to gas takes place. Above 373 K, X exists in gaseous state. At QR (273 K), interconversion of solid to liquid takes place so, matter exists both in solid and liquid states and it represents latent heat of fusion. At ST (373 K), interconversion of liquid to gas takes place so, matter exists in both liquid and gaseous states and it represents latent heat of vaporisation. Temperature remains constant at QR and ST.