Q.Match the following graphical variation with their description
Column A: (i)

The key idea is that in a reversible reaction, reactant concentration falls and product concentration rises until both become constant at equilibrium.

Step 1 – Reactant curve: A reactant starts at a high concentration and decreases as it is consumed. The curve flattens when the forward and reverse rates become equal, so the concentration stops changing. This matches (i) and (iii), which are essentially the same description.

Step 2 – Product curve: A product starts near zero and increases as it is formed. It also flattens at equilibrium. This matches (ii). …

The core idea

When a reversible reaction proceeds, the concentrations of reactants and products change until they reach a dynamic equilibrium. A graph of concentration vs. time reveals two things at a glance: the direction of change (up or down) tells you whether the species is a product or a reactant, and the flattening of the curve tells you that equilibrium has been reached.

At equilibrium, the forward and reverse rates become equal, so the net change in concentration of every species is zero. That is why the curve becomes horizontal — parallel to the time axis — and stays there.

Matching each graph

1. Graph (i): starts high, decreases, levels off

A species that begins at a high concentration and then falls must be a reactant — it is being consumed as the reaction moves forward. The curve flattens when the reaction reaches equilibrium, meaning the reactant is no longer being used up on net. This matches description (c).

2. Graph (ii): starts near zero, increases, levels off

A species that starts near zero and rises must be a product — it is being formed as the reaction proceeds. The flat region again signals equilibrium, where the product concentration stops changing. This matches description (a).

3. Graph (iii): falls from a higher value, then becomes constant …