Question

What is a node $$?$$

Answer 1

Hint: The square of the wave function, $${\psi }^2$$, represents the probability of finding an electron in a given region within the atom. An atomic orbital is a mathematical function describing the location and behaviour of an electron in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom’s nucleus.
There four types of orbitals are sharp, principle, diffuse and fundamental (that are familiar with s, p, d and f). Within each shell of an atom there are some combinations of orbitals.

Complete answer:
Node is a point where the electron probability is zero. For a given orbital, the two types of nodes are radial node and angular node.
Radial node is a spherical surface where the probability of finding an electron is zero. The number of radial nodes increases with the principal quantum number ($$n$$). Radial node is also called a nodal region.
Angular node is a plane that passes through the nucleus. Angular node is equal to the azimuthal quantum number ($$l$$). Angular node is also called a nodal plane.
For any given orbital, the number of radial nodes is equal to $$n-l-1$$, the number of angular nodes is equal to $$l$$.
Then the total number of nodes is equal to $$n-1$$.

Note:
In quantum mechanics, the azimuthal (or orbital angular momentum) quantum number describes the shape of a given orbital. It is denoted by the symbol '$$l$$’ and its value is equal to the total number of angular nodes in the orbital. The principal quantum number is one of four quantum numbers assigned to each electron in an atom to describe that electron's state. Its values are natural numbers.