If there is a solution of chloroform and alcohol, each in proportion of 50 ml and 50 ml to form a solution of 100 ml, then which one is the solvent and why?

Chloroform is a chemical with the formula CHCl3.  It is a clear liquid and is commonly used as a solvent in organic chemistry.  Alcohol is a generic term for any alcohol but is probably most commonly used as a shorthand for ethyl alcohol (CH3CH2OH).  It is also a clear liquid that is a common solvent in chemistry.  If we mix 50 mL of each of the two chemicals, then we have an equal mixture of both.  The two liquids are miscible with each other and will combine to form a homogeneous mixture.  Since the two are present in equal proportions, we would say that the solvent system is a 1:1 mixture of chloroform and ethanol.  Since they are equal neither of them gets precedence over the other.
https://www.thoughtco.com/definition-of-solvent-604651