Answer:
B. Mg + ⇒ MgS +
Explanation:
There are several types of chemical reactions depending on the reaction mechanisms: combination, single-displacement, double-displacement, combustion, decomposition, combustion and redox reactions.
In this case we have a single-displacement reaction, which means that a new chemical species (Mg) replaces other (H) in a given chemical compound (). It happens because the electronegativity of H (a nonmetal) is greater than the Mg electronegativity. Thus H attracts the electrons strongly.
That's why there is a transference of electrons from Mg to . We can say that Mg reduces .
Once is reduced to H, a covalent bond is formed between two hydrogen atoms, and then is released as a gas.