In a complexometric titration of metal ion with ligand M (Metal ion) + L(Ligand) $$\rightarrow$$ C (Complex). End point is estimated spectrophotometrically (through light absorption). If 'M' and 'C' do not absorb light and only 'L' absorbs then the titration plot between absorbed light (A) versus volume of ligand 'L' (V) would look like:

The complexometric titration follows

$$M + L \;\longrightarrow\; C$$

Given information about absorption of visible / UV-light:

• The metal ion $$M$$ does not absorb.
• The complex $$C$$ does not absorb.
• The ligand $$L$$ is the only species that absorbs.

Let the absorbance recorded by the spectrophotometer be $$A$$. According to Beer-Lambert law, when the path-length is fixed,

$$A \;=\; \varepsilon\,c_L\,l$$

where $$c_L$$ is the concentration of free (uncomplexed) ligand in the solution at that instant.

Before the equivalence point

• Each small volume increment $$\Delta V$$ of ligand added is completely consumed by the metal ion to form the colourless complex $$C$$.
• Therefore the concentration of free ligand remains zero: $$c_L = 0$$.
• Consequently the absorbance stays at $$A = 0$$, irrespective of the volume added.

At the equivalence point

• The number of moles of ligand added exactly equals the number of moles required to bind all the metal ions present.
• Still, no free ligand is present, so $$A = 0$$ just up to this point.

Beyond the equivalence point

• The metal ion is already saturated; any further ligand remains unreacted in solution.
• The concentration of free ligand is now proportional to the excess volume added: $$c_L \propto V - V_{\text{eq}}$$.
• Hence the absorbance increases linearly with the additional volume: $$A \propto (V - V_{\text{eq}})$$.

Combining the three regions, the $$A$$-vs-$$V$$ plot is

• A horizontal line at $$A = 0$$ from $$V = 0$$ to the equivalence volume $$V_{\text{eq}}$$, and
• A straight line with positive slope starting at $$V_{\text{eq}}$$ and rising linearly thereafter.

This corresponds to the diagram shown in Option A.

Therefore, the correct choice is:
Option A which is the described plot.