What would be the number of chromosomes in the aleurone layer if the megaspore mother cell contains 10 chromosomes?

The correct option is B c. 15
Aleurone layer
The aleurone layer is the outer layer of the endosperm. As the endosperm is developed from triple fusion, it is triploid in nature, i.e., it contains three sets of chromosomes.

Megaspore mother cell
Megaspore mother cells are diploid sporogenous cells present in the megasporangium or ovule.

Chromosome number in aleurone layer
If the diploid megaspore mother cell contains 2n = 10 chromosomes, then n = 5 chromosomes.
Triploid aleurone layer cells will contain 3n = 15 chromosomes.

Final answer
c. 15.