What part of the atom is involved in chemical bonding with other atoms? the protons in the nucleus the innermost electron shell the neutrons in the nucleus the outermost electron shell

The correct answer is the outermost electron shell.

The outermost electron shell, or valence electron shell, is involved in chemical bonding with other atoms. It is for this reason that groups on the periodic table (columns of elements like the nobles gases) have similar properties; their similar chemical properties arise from the fact that they have the same number of valence electrons. Valence electrons are involved in bonding because each atom looks to have a complete valence shell. For some elements, this is most easily obtained by losing electrons (making a cation, or positive ion). For other elements, this is most easily obtained by gaining electrons (making an anion, or a negative ion).

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i'd say that the moon rock is about 2.2 billion years old.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).