In the periodic table metals usually used as catalyst belongs to
A. F-block
B. D-block
C. S-block
D. P-block

Hint: Catalyst is a substance that alters i.e. increases the rate of the reaction without getting consumed in the process. Catalysts normally speed up a reaction by decreasing the activation energy or altering the reaction mechanism. Catalysts generally belong to the transition metal group due to the availability of their vacant d orbital.

Complete step by step solution:
● We know that catalysts are not going to be consumed in the chemical reactions.
● In a lot of reactions, D-block elements mean transition metals or elements are used as catalysts. Transition metals, for example, nickel, platinum, chromium, cobalt, iron, etc., are used as catalysts.
● The catalytic property for d-block elements are due to
(a) Availability of vacant d-orbitals
(b) Ability to show various oxidation states.
(c) Ability to form transition states in the chemical reaction.
(d) Ability to form complex compounds with the ligands.
● Catalysts generally lower or decrease the activation energy barrier to increase the rate of reaction.
● For example in the synthesis of ammonia through Haber’s process, finely divided iron is used as a catalyst.
● Titanium tetrachloride is used in the preparation of high-density polythene (HDP).

So, the correct option is B.

Note: Don’t be confused that all D-block elements are not catalysts. Few elements or metals because of their variable oxidation states show the property as a catalyst.
Few catalysts will show the property to decrease the rate of a chemical reaction that is called quenchers.