You know that neutrons are found in the nucleus of an atom. Under normal conditions, protons and neutrons stick together in the nucleus. During radioactive decay, they may be knocked out of there. Neutron numbers are able to change the mass of atoms, because they weigh about as much as a proton and electron together.
Explanation:
protein is the element responsible for building up of cells and the nucleic acid is embedded in the cell, so protein builds the whole cell including the nucleic acids.. the nucleic acid is also packed by histones which is a proteinous structure. both are important because, in the cell all organelles require protein for their growth and likewise the encoding of the genetic information carrier
D. Electrons because isotopes deal with electrons.
C.) Rocks in the Geosphere
Hope this helps :)