Which of the following characteristics indicates that an atom is unstable?

I think is d.

Explanation:

particles that make up the nucleus are balanced. An atom is unstable (radioactive) if these forces are unbalanced; if the nucleus has an excess of internal energy. the Instability of an atom's nucleus may result from an excess of either neutrons or protons.

I'm not sure, but hope it helps.

c. 75.7

i think that is the right

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.