According to me A is the answer
Answer:
79 g/mol
Explanation:
Mass of unknown metal deposited = 3.137 g - 1.4 g = 1.737 g
Number of moles of metal deposited = 0.022 moles
Since;
Number of moles = reacting mass/molar mass
Molar mass = reacting mass/number of moles
Molar mass = 1.737 g/0.022 moles
Molar mass= 79 g/mol
You should have given us a table, but I think my table shouldn't be too different.
Let's put oxidation numbers first.
You would have to know that Mg(s) is a reducing agent and Br2(l) is an oxidizing agent. But it is pretty common knowledge that the halogens will tend to take the electrons and alkali and alkaline earth metals will tend to give up electrons.
Mg is oxidized because it gives up electrons; Br2(l) is reduced because it gains electrons. Since the reaction conforms to what we would expect to <em>naturally</em> (thermodynamically favored) occur, it can take place given that the activation energy is supplied.