What is conserved in this reaction?

N2 (g) + 3F2 (9)

2NF: (9)

O mass and atoms

O moles only

O atoms only

O mass only

First option: mass and atoms.

Explanation:

In that reaction, and in every chemical reaction, mass and atoms are conserved.

The law of conservation of mass is universal: the mass cannot either be created or destroyed, so this is a valid principle that you must apply to both physical and chemical changes.

Also, atoms are not either created or destroyed during chemical reactions, they are rearranged: some bonds of the reactants (left side of the equation) are broken and new bonds are formed to make new products (right side of the equation), but at the end the same atoms in kind and number are in present in both sides.

Your reaction is:

N₂ (g) + 3F₂ (g) → 2NF₃ (g)

Which you may read as:

1 mol of diatomic nitrogen gas reacts with 3 moles of diatomic fluorine gas to form 2 moles of nitrogen fluoride gas.

When you analize that, there are 2 moles of atoms of nitrogen on each side and 6 moles of atoms of fluorine on each side, so both atoms and mass are conserved, but there are 1 + 3 = 4 moles of reactants (left side) and 2 moles of product (right side), meaning that moles are not conserved.