Match List-I with List-II:
List-I                                       List-II
(a) Chlorophyll                       (i) Ruthenium
(b) Vitamin-B$$_{12}$$                 (ii) Platinum
(c) Anticancer drug               (iii) Cobalt
(d) Grubbs catalyst               (iv) Magnesium
Choose the most appropriate answer from the options given below:

We need to match each substance with the metal it contains.

Chlorophyll is the green pigment in plants responsible for photosynthesis. Its porphyrin ring contains a central magnesium ($$\text{Mg}$$) ion, so (a) matches with (iv).

Vitamin $$\text{B}_{12}$$ (cyanocobalamin) is an organometallic compound that contains cobalt ($$\text{Co}$$) at its centre, so (b) matches with (iii).

The most famous anticancer drug is cisplatin, $$[\text{PtCl}_2(\text{NH}_3)_2]$$, which is a coordination compound of platinum ($$\text{Pt}$$), so (c) matches with (ii).

Grubbs catalyst is widely used for olefin metathesis reactions and is a ruthenium ($$\text{Ru}$$) based organometallic complex, so (d) matches with (i).

Therefore the correct matching is: a-iv, b-iii, c-ii, d-i, which corresponds to Option B.