Answer : The correct option is, (C) metal corroding in salt water
Explanation :
Physical change : It is a change where no new compound or substance is formed. In this, changes occurs only in the phase.
Chemical change : It is a change in which a new compound or substance is formed and releases some energy. There is no changes occurs in the phase.
(A) Mixing of poster colors : It is not a chemical change. It is a physical change because in this process no new substance is formed.
(B) Formation of clouds : It is not a chemical change. It is a physical change because in this process only phase changes from gaseous state to liquid state.
(C) Metal corroding in salt water : It is a chemical change because a new compound or substance is formed by the corroding the metal.
(D) Sugar dissolving in water : It is not a chemical change. It is a physical change because in this process no new substance is formed.
(E) Separating salt from seawater : It is not a chemical change. It is a physical change because in this process no new substance is being formed.
Hence, the metal corroding in salt water is a chemical change.