Question

What does Pt mean in a chemical reaction?

Answer 1

Chemical elements were represented by some small notations or starting letters of the name of the elements which are known as chemical symbols. The chemical symbol for the platinum element is Pt, which can be used mostly as a catalyst in the reactions involving hydrogen and oxygen gas.

Complete answer:
Periodic table consists of a total of $118$ elements arranged in the increasing order of atomic numbers in vertical columns and horizontal rows. The vertical columns were known as groups and the horizontal rows are known as periods. There is a total of $7$ periods and $18$ groups in the periodic table.
The elements belonging to ${11^{th}}$ group were Nickel, Palladium and Platinum. These three elements are mostly used as catalysts in the chemical reactions involving oxygen gas and hydrogen gas.
Platinum looks like silver metal, the Latin meaning of platinum is little silver. Platinum is a lustre metal. It is an element with atomic number $78$ which can be used as a catalyst. Thus, in chemical reactions Pt means platinum which acts as a catalyst by allowing more surface area to break the bonds of oxygen and hydrogen gases.

Note:
In some reactions belonging to electrochemistry, platinum can be used as an electrode, it can be written as Pt in brackets. When it is written before the two vertical lines, it acts as an anode and when it is written after the two vertical lines it acts as a cathode.