Question

A single orbital in the 3d level can hold how many electrons?

Answer 1

Orbitals. An orbit is the simple planar representation of an electron.
An orbital refers to the dimensional motion of an electron around the nucleus in a three-dimensional motion around which the probability of finding an electron is maximum.
It can be simply defined as the path that gets established in a circular motion by revolving the electron around the nucleus.

Complete step by step answer:
Orbitals that have the same value of the principal quantum number n form a
shell. Orbitals within a shell are divided into subshells that have the same value of the
angular quantum number l. Chemists describe the shell and subshell in which an orbital belongs with a two-character code such as 2p or 4f.

Shell name	Subshell name	Subshell max electrons
M	$3s$ $3p$	$2$ $6$
N	$\mathbf{3d}$ $4s$	$10$ $2$

The closest orbital to the nucleus, called the $\mathbf{1s}$ orbital, can hold up to two electrons. This states that in the ground state of an atom or ion, electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels. For example, the $1s$ subshell is filled before the $2s$ subshell is occupied. is equivalent to the innermost electron shell of the Bohr model and Hund's rule of maximum multiplicity explains the filling of orbitals in the subshells. ... Each orbital can hold a maximum of two electrons of the atom.
The $\mathbf{n}$ and $\mathbf{l}$ in the $\left( n+l \right)$ rule are the quantum numbers used to specify the state of a given electron orbital in an atom. $n$ is the principal quantum number and is related to the size of the orbital. l is the angular momentum quantum number and is related to the shape of the orbital.

Note: Knowing these types of ques helps to understand and solve electronic configuration type ques.It is important to understand postulates of bohr model and hund’s rule of maximum multiplicity.