The correct option is 2 and 3 only.
Explanation
Oxidation and reduction reactions, collectively termed redox reactions, are fundamental chemical processes defined by the transfer of oxygen, hydrogen, or electrons between substances.
Statement-wise Analysis:
- Statement 1 is Incorrect: Oxidation is defined as the addition of oxygen to a substance or the removal of hydrogen from a substance. It is not defined as the removal of oxygen; the removal of oxygen is termed reduction. Furthermore, the definition is not exclusive to oxygen transfer, as it also encompasses electron transfer.
- Statement 2 is Correct: Reduction involves the removal of oxygen from a substance. For example, when a metal oxide loses oxygen to form the metal, the process is classified as reduction.
- Statement 3 is Correct: Reduction is characterized by the addition of hydrogen to a substance. Conversely, the removal of hydrogen is classified as oxidation.
- Statement 4 is Incorrect: In terms of electronic theory, oxidation involves the loss of electrons by an atom or ion. The gain of electrons is defined as reduction.
Key Takeaway:
Oxidation is the gain of oxygen, loss of hydrogen, or loss of electrons. Reduction is the loss of oxygen, gain of hydrogen, or gain of electrons.