Which would you most expect to be an unstable atom?

a carbon (c) atom with 6 protons and 6 neutrons

an iron (fe) atom with 26 protons and 27 neutrons

a helium (he) atom with 2 protons and 2 neutrons

a curium (cm) atom with 96 protons and 85 neutrons

Option (d) is the correct answer.

Explanation:

In a nucleus, there exists both protons and neutrons whereas electrons revolve around the nucleus.

Protons are positively charged whereas neutrons have no charge. Since protons have positive charge so they repel each other generating electrostatic force of repulsion.

Whereas neutrons form a nuclear binding energy which helps to overcome this electrostatic force of repulsion and therefore, binds the protons and neutrons together in a nucleus.

So, when there are more number of protons than neutrons then the atom will become unstable because then nuclear binding energy cannot overcome the electrostatic force of repulsion of protons.

Thus, we can conclude that out of the given options, a curium (Cm) atom with 96 protons and 85 neutrons would be expected to be an unstable atom.

the pull of gravity on the rocket decreases