Which of these could be a physical change?
a. wood is burned in a fireplace.
b. cake batter is baked in an oven.
c. a blue liquid and a yellow liquid mix and make a green liquid.
d. baking soda is mixed with vinegar to make carbon dioxide gas.

C

Explanation:

A physical change is when the form of the matter is just altered. While a chemical change results from a chemical reaction. No reaction is happening during the mixing of the two colors [nothing is boiling, freezing, evaporating, melting ext.] , but after you mix them the end result does look different. That only because we changed the physical properties of it.

(B is not a physical change because the baking powder inside of the cake must under go a reaction that causes the cake to rise. )

C. A blue liquid and a yellow liquid mix and make a green liquid.

Explanation:

A physical change is a change in which chemically a substance remains the same but a change in state of matter may occur. It is a reversible change i.e. the substance can be converted into the original state even after the change has occurred. As per option c even if a blue liquid has been mixed with a yellow liquid to produce a green liquid we can still separate both the liquids using a physical method of separation to get the original liquids back.

Other options are wrong because they are examples of chemical change in which the change is irreversible and we can never get the original substance back by any means because a reaction has changed the substance entirely.

not clear

the answers would be

the first one and the second one