Chemistry · Redox Equilibrium · NEET
Reduction is addition of HYDROGEN, not oxygen. Adding oxygen is oxidation. So the two rules for reduction are: (1) remove oxygen, or (2) add hydrogen. Students often flip these, so remember: reduction removes oxygen but adds hydrogen. Example of adding hydrogen: CH2=CH2 + H2 gives C2H6 (ethene is reduced to ethane).
The classical (oldest) concept looks only at oxygen and hydrogen atoms. A substance is reduced if oxygen is taken away from it, or if hydrogen is added to it. Later this was broadened to include removal of any electronegative element or addition of any electropositive element. NEET may ask you to spot reduction using just this simple oxygen/hydrogen rule.
When mercuric oxide is heated, it breaks down: 2HgO gives 2Hg + O2. The oxygen leaves the mercury. Because oxygen is REMOVED from HgO, we say HgO is reduced to mercury metal. This is the standard NCERT example of reduction by removal of oxygen.
Yes. In 2FeCl3 + H2 gives 2FeCl2 + 2HCl, chlorine (an electronegative element) is removed from ferric chloride. Removing an electronegative element counts as reduction in the broadened classical concept, the same way removing oxygen does. So FeCl3 is reduced to FeCl2.
Reduction never happens alone. Whenever one substance is reduced (gains hydrogen or loses oxygen), another substance is oxidised at the same time. This is why we call these reactions redox reactions. For example, when HgO loses oxygen, look for what took that oxygen or what got oxidised in the full equation.
They are exact opposites. Oxidation = add oxygen OR remove hydrogen. Reduction = remove oxygen OR add hydrogen. So if you know one, just reverse it for the other. In one reaction, one species follows the oxidation rule and the other follows the reduction rule.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Because the earliest chemists studied metal oxides. When they pulled oxygen out of an oxide to get the pure metal, they called it reduction. Example: 2HgO gives 2Hg + O2, so HgO is reduced when its oxygen is removed.
CH2=CH2 + H2 gives H3C-CH3. Hydrogen is added to ethene, so ethene is reduced to ethane. This is important for NEET organic and redox questions.
Yes. The classical idea was broadened. Removing any electronegative element (like chlorine) is reduction, just like removing oxygen. Example: 2FeCl3 + H2 gives 2FeCl2 + 2HCl, where chlorine is removed from FeCl3.
NEET often gives a simple reaction and asks which species is reduced. Using the classical oxygen/hydrogen rule is the fastest way to answer without calculating oxidation numbers. It also builds the base for the electronic and oxidation-number concepts that come next.
