The compound which shows metamerism is:

For the following four structures $I$ to $IV$,which statement is correct?
$(I)$ $C_2H_5-CH(CH_3)-C_3H_7$
$(II)$ $C_2H_5-CO-CH(CH_3)-C_2H_5$
$(III)$ $CH_3^+$ (Methyl carbocation)
$(IV)$ $C_2H_5-CH(CH_3)-C_2H_5$

Which of the following pairs are not isomeric compounds?

The two compounds $CH_3-CH_2-C(=O)-CH_2-CH_2-CH_3$ and $CH_3-C(=O)-C(CH_3)_2-CH_3$ can be classified as:

Compounds having the same molecular formula but different structural formulas are called ........

Which of the structures is/are diastereomer of $A$?