Solution

Color blindness in X-linked recessive disease. A man whose father was colour blind (XcY) and mother was normal (XX; we will consider normal unless mentioned otherwise), is normal (XY; as he is getting normal X from the mother and Y from the father).
Woman who had a colour blind mother (XcXc) and normal father (XY), will be the carrier (XcX; as she is getting one Xc from the mother and another X from the father).
The offspring resulting from this couple (XcX and XY are :
XcX, XcY, XX, XY.
Out of these four, 2 of them are males (XcY, XY) of which one is colour blind (XcY). So, the chances of the male child to be colourblind is 50%.
Thus, the correct answer is option (C), '50%'.