Alright, so here's the deal. When we're talking about chemical changes, we're looking for something where the actual stuff (like the molecules and atoms) changes into something totally different. It's like turning into a completely new thing. On the other hand, physical changes are just about changing shape or state, but the stuff itself stays the same.
Now, let's break it down:
a. Casting iron from a blast furnace - This is about melting and shaping iron. The iron is still iron, so it's a physical change.
b. Distilling whisky from fermented barley - This is about separating liquids based on boiling points. Again, no new stuff is made, just separating what's already there. So, it's physical.
c. Mixing acid with alkali causing a temperature rise - Bingo! Here, the acid and alkali react and totally transform into new substances (like salt and water). That's a chemical change for sure.
d. Freezing animal tissue in liquid nitrogen - This is just about changing the state from liquid to solid. The tissue is still the same stuff, just frozen. So, it's a physical change.
So, the one that's a chemical change? It's "c. Mixing acid with alkali causes a temperature rise". The others are just about changing looks or states, not making new substances.
