Which of the following characterizes nuclear reactions?
the loss of mass cannot be accounted for.
the chemical composition of the atoms remains the same.
the number of protons and neutrons in reacting atoms changes.
energy is not conserved.

The number of protons and neutrons in reacting atoms changes.

Explanation:

Typical of all nuclear reactions is the change that occurs within the nucleus of the atom. In a nuclear reaction, the number of protons and neutrons changes to form a new atom.

What drives a nuclear reaction is the stability ratio between the neutron and protons. Every atom has its stability ratio. A nucleus with a neutron/proton combination different from the stability ratio will be unstable and split into one or more other nuclei. Therefore, a nuclear reaction occurs to maintain and ensure that the stability ratio is maintained and achieved.

out of these options:

ability to burn paper

pure sodium reacting violently with water

the boiling point of water

helium does not tend to react with anything

i would say this is a physical property:

helium does not tend to react with anything

why? :

i said helium does not tend to react with anything because well, it reacts to ! but ability to burn paper, pure sodium reacting violently with water, & the boiling point of water are chemical or

physical properties: the properties of a substance that can be observed without changing the chemical makeup of the substance

chemical properties: properties of a substance relating to the chemical nature and reactivity of the substance