Question

2.which part of the atom allows one atom to react with another one?

Explanation:

Atoms react with each other mainly due to the electrons in their outermost electron shells. The outermost electrons (valence electrons) are involved in chemical bonding. For example, in ionic bonding, atoms transfer valence electrons, and in covalent bonding, atoms share valence electrons.

Answer:

The outermost electrons (valence electrons) of the atom.