2Al(s)+6HCl(aq)➡️2AlCl3(aq)+3H2(g)
What are the oxidation numbers for elements on both sides of the equation? which element is being oxidized and which is being reduced?
Al is zero on the left and 3+ on the right. Loss of 3 electrons/atom
H is 1+ on the left and 0 on the right. Gain of 1 electron/atom
Cl is 1- on the left and 1- on the right. No change.
Oxidation is the loss of electrons. Reduction is the gain of electrons.