Some statements are given with regard to entropy. The incorrect statements are 

a) The absolute entropy of substances cannot be determined 

b) In standard state entropy of elements is always positive 

c) The entropy of universe always decreases 

d) In a spontaneous process, for isolated system, the entropy of a system generally increases

 Statement a) the absolute entropy of substances cannot be determined is incorrect because the third law of thermodynamics gives a fixed reference point that allows us to measure the absolute entropy of any substance.

Statement c) the entropy of the universe always decreases is incorrect because the entropy of the universe always increases.

Therefore, option C is correct.