Question

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how do atoms form a new substance?
by sharing electrons with each other
by gaining electrons from each other
by losing electrons
by losing neutrons to each other

Explanation:

Atoms form new substances through chemical bonding. Covalent bonds occur when atoms share electrons, ionic bonds when one atom gains electrons from another, and metallic bonds involve a sea - of electrons. Sharing electrons is a common way in covalent compounds. Losing or gaining neutrons is not a typical way of forming new substances as it affects the isotope of an atom rather than chemical bonding. Losing electrons alone doesn't fully explain formation of new substances without a corresponding electron - accepting atom. Gaining electrons from each other is not a complete or common description compared to sharing in covalent bonding.

Answer:

by sharing electrons with each other