Question

which of the following are physical changes that may have occurred in this image?
water reacted with calcium carbonate to form calcium oxide to make the concrete on the bridge.
none of these are physical changes.
the fallen leaves started to decompose.
the leaves changed color from green to red, orange, and yellow.

Explanation:

A physical change is a change in which no new substances are formed. The change in leaf color is due to the breakdown of chlorophyll (a natural process in autumn) and is a physical change as no new chemical substances are formed. Decomposition of leaves is a chemical change (involving breakdown by microbes to form new substances like humus). The reaction of water with calcium oxide to form calcium hydroxide (and then with carbon dioxide to form calcium carbonate in concrete) is a chemical reaction (new substances formed).

Answer:

The leaves changed color from green to red, orange, and yellow.