How to pronounce
I noticed that there's a difference in the pronunciation of the word "Excuse"
e.g 1) when someone hit someone accidently, the person says " excuse me" without pronouncing the letter 'c'
2)when someone is late for class, the teacher asks "whats your excuse?" and here excuse is pronounced with the letter 'c' as 'k'
Someone please tell me if im right or not

Question

How to pronounce
I noticed that there's a difference in the pronunciation of the word "Excuse"
e.g 1) when someone hit someone accidently, the person says " excuse me" without pronouncing the letter 'c' 
2)when someone is late for class, the teacher asks "whats your excuse?" and here excuse is pronounced with the letter 'c' as 'k' 
Someone please tell me if im right or not

Answer

So basically 'excuse' as in the verb, is pronounced with more of a 'z' sound at where the 's' is.

'excuse' as is the nous, i.e: what's your excuse?; is proposed with an 's'

Answer

I agree with the two answers above. Additionally I don't think there is a pronunciation change between the c sounds of the two words.

Answer

As Shahin correctly said, the first example you gave with 'excuse' is pronounced with a Z, so it sounds like "ek-skewzzz", whereas the second 'excuse" is more with an S sound e.g. "ek-skewsss"