The alkane that yields two isomeric mono-bromo derivatives

Neopentane contains only one type of hydrogens and forms only one type of mono bromo alkane.

Ethane contains only one type of hydrogens (i.e., 'A') hence it forms only one type of mono bromo alkane.

Methane also contains only one type of hydrogen,hence it too forms only one type of mono bromo derivative.

It has two types of hydrogens (1⁰ and 2⁰ ) and hence it forms two types of mono bromo derivatives.