According to the explanation about oxidizing and reducing agents from the previous session, we will find the answers to this question as well
Oxidation numbers are mostly found in previously made tables, there are plenty of tables where you can see the oxidation numbers for almost every element, a few rules to have in mind is H is usually +1, O is -2, Halogens are -1, group 1A metals are +1, transition metals are the ones that will shift a lot
1. Sn + 2 HCl -> SnCl2 + H2, this is the properly balanced equation
REACTANTS
Sn = 0, since it's a lone element in the reaction we assume its charge is 0 because is stable
H = +1
Cl = -1, it's a halogen
PRODUCTS
Sn = +2, we see now that Sn was oxidized and now has a positive charge
Cl = still -1
H2 = 0, was reduced, now with a 0 charge
2. 2 NaBr + Cl2 -> 2 NaCl + Br2
REACTANTS
Na = +1, metal from group 1A
Br = -1, halogen
Cl2 = 0 stable element
PRODUCTS
Na = +1
Cl = -1, it will be reduced
Br = 0, it will be oxidized
3. SiCl4 + 2 Mg -> 2 MgCl2 + Si
REACTANTS
Si = +4
Cl = -1
Mg = 0
PRODUCTS
Mg = +2, it will be oxidized
Cl = -1
Si = 0, it will be reduced