Ur ques seems to be a bit faulty but still probable answers cud be-

For molecular mass=54, see the nearest no of C possible, i.e. 4, as 12x4=48 and rest can be 6H atoms to make the formula C4H6, that is an alkyne.

Now to find whether it is a terminal or internal alkyne, start backwards.

D on ozonolysis gives E which is a diketone and which on oxidation gives only ONE product, propanoic acid. As it is a diketone and still giving only one product, it means it must be a symmetric diketone otherwise it wud hav given 2 diff. acids.

For it to be symmetric, A has to be terminal.

SO, A----> CH3-CH2-CCH.

 

C---> CH3-CH2-CH2-CH3

 

For D,

A+CH3CH3Br + NaNH2------> CH3-CH2-CC-CH2-CH3

 

Most probably, E is----> CH3-CH2-C-C-CH2-CH3

 

Acc to the data given by U, there is some doubt in B. It shud be 593% heavier not 493% taking mass of Br=80.

 

But still B-------> CH3-CH2-C(Br)₂-C(Br)₂

It shud be a double halogenation reaction.

 

Hope U understand.