Answer
a) Oxygen and b) Bromine are expected to be good oxidizing agents here based on periodic trends.
Work Step by Step
Oxidizing agents are those substances or elements which have tendencies to gain electron and become reduced in a reaction and helps other substance to become oxidized.
a. Oxygen: Oxygen is a non-metal (grp. 16 element in the periodic table). So, it has tendency to gain electron from other substance in a reaction and become reduced. So, it is a good oxidizing agent.
b. Bromine: Bromine is a non-metal (group 17 element in the periodic table). So, it has the tendency to gain electron and become reduced. So, it is a good oxidizing agent.
c. Lithium: Lithium is a metal (group 1 element in the periodic table). Metals have the tendencies to lose electron and become oxidized. So, it is a good reducing agent rather than a good oxidizing agent.
d. Sodium: Sodium is a metal (Grp. 1 element in the periodic table). So, it also has the tendency to lose electron and become oxidized. So, it is a good reducing agent rather than a oxidizing agent.
