Answer:
A nucleus that contains 10 protons and 10 neutrons
Step-by-step explanation:
as we know that nuclear stability depends on various factors out of which first part on which stability depends on is N/P ratio
if N/P ratio lie between 1 and 1.2 then nuclei is a stable nuclei and if the ratio of N/P is greater than 1.2 then it is unstable.
As the number of protons increases then the number of neutrons must be more than number of neutrons so that mutual repulsion force of protons are counter balanced.
Next parameter is even combinations of neutrons and protons are always more stable than odd combinations of neutrons and protons
So correct answer will be
A nucleus that contains 10 protons and 10 neutrons