Final answer:
B .substitutional .alloy is an alloy in which the composition of the elements is variable and one element has a much smaller radius than the other.
Step-by-step explanation:
The alloy described in the question is a substitutional alloy.
In a substitutional alloy, the atoms of one element replace the atoms of another element in the crystal structure. In this specific case, the composition of the elements is variable, and one element has a much smaller radius than the other. This means that the smaller atoms can easily replace the larger ones without significantly affecting the crystal structure.
For example, brass is a type of substitutional alloy made by replacing some of the copper atoms in the crystal structure with zinc atoms. The zinc atoms have a smaller radius than the copper atoms, allowing them to fit into the crystal lattice without causing major distortions.