Which statement about a chemical reaction is true? it occurs only at low temperatures. it occurs only at high temperatures. it occurs whenever a physical change takes place. it occurs whenever a chemical change takes place.

Option (d) is the correct answer.

Explanation:

A reaction which causes a change in the rearrangement of atoms or chemical composition of a substance is known as a chemical change.

A chemical change can take place rapidly, slowly or too slowly.

For example, rusting of iron is a slow chemical change.

Therefore, the statement which is true about a chemical reaction is that it occurs whenever a chemical change takes place.

The correct statement is it occurs whenever a chemical change takes place.

Explanation:

A physical reaction is defined as the reaction in which a change in shape, size takes place. No new substance gets formed in these reactions.

A chemical reaction is defined as the reaction in which a change in chemical composition takes place. A new substance is formed in these reactions.

These reactions can happen at any temperature. Like in cold conditions, Azo dye is prepared and at high temperatures, dissociation of water takes place.

Thus, a chemical reaction occurs only when a chemical change takes place in a substance.

Hence, the correct statement is it occurs whenever a chemical change takes place.

the leaf is an organ of a typical plant, and the main functions are to complete photosynthesis and allow the plant to exchange gas, just like how we have the respiratory system. leaves have the stomata, which collects maintains co2 and o2 levels. this is necessary for cell metabolism. the leaf also collects sunlight using chloroplasts. succinctly, leaves own a pivotal role in sustaining plant life.

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.