How does the law of conservation of mass apply to this reaction: mg + hcl + h2 + mgcl2 ?
hydrogen and chlorine need to be balanced. there is an equal amount of magnesium
on each side
the equation needs to be balanced. there are fewer hydrogen atoms in the equation
than magnesium or chlorine.
the law of conservation of mass has already been applied. there is an equal number
of each element on both sides of the equation.
only the hydrogen needs to be balanced. there are equal numbers of magnesium and
chlorine
finish

Hydrogen and chlorine need to be balanced. There is an equal amount of magnesium on each side.

Explanation:

The given chemical equation does not hold the law of conservation of mass because the number of atoms of hydrogen and chlorine are not balanced on each side.

Chemical equation:

Mg + HCl  → MgCl₂ + H₂

Balanced chemical equation:

Mg + 2HCl  → MgCl₂ + H₂

Now this equation hold the law of conservation of mass.

Law of conservation of mass:

According to the law of conservation mass, mass can neither be created nor destroyed in a chemical equation.

Explanation:

This law was given by french chemist  Antoine Lavoisier in 1789. According to this law mass of reactant and mass of product must be equal, because masses are not created or destroyed in a chemical reaction.

its first and third is your answer i did the qustion the fourth isnt right