The correct option is C Assertion is correct but Reason is incorrect.
Slime moulds are unicellular organisms. However, under stress situations, they come together into a cluster that behaves as one organism. These organisms show division of labour. In these organisms, some cells form fruiting bodies and other cells form spores inside the sporangia. Hence they were called primitive fungi and were grouped in Mycetozoa. Thus the correct answer is option C.