Yes all are correct
a-
some element like Cr ,Cu,Gd etc shows uncommon electric configurations
when we do ec of Cr ,actually last electron should enter 4s2 but we know half filled orbital are more stable and similar for fully filled in case of cu
therefore for stability it has configuration of 3d5,4s1
b
it's ans lie on ec of k which is
[Ar]4s1 which shows it can have 1/2 spin quantum no
there are some formulas also to find
c
ans for c and d is similar as p have 3 sub orbital and shave 1 sub orbital
and 1 sub orbital can have max 2 electron

no of sub orbital is( 2n-1) where n is principal quantum no

A) The electronic configuration Cr is [Ar] 3d5,4s1
The atomic number of chromium (Cr) is 24. The electronic configuration of an atom represents the distribution of electrons in its energy levels or orbitals.

- The noble gas before chromium is argon (Ar), which has the electronic configuration [Ne] 3s2, 3p6.
- The atomic number of chromium indicates that it has 24 electrons.
- The electronic configuration of chromium can be written as [Ar] 3d5, 4s1. This means that the 3d orbital has 5 electrons, and the 4s orbital has 1 electron.

b) Spin quantum number of K (19) can have a value of -1/2
The spin quantum number describes the spin orientation of an electron in an orbital. It can have two possible values: +1/2 or -1/2.

- The atomic number of potassium (K) is 19.
- Each electron in an atom is described by four quantum numbers: the principal quantum number (n), the azimuthal quantum number (l), the magnetic quantum number (m), and the spin quantum number (s).
- The spin quantum number (s) can have a value of +1/2 or -1/2.

Therefore, the spin quantum number of potassium (K) can indeed have a value of -1/2.

c) Any p-orbital can have a maximum of two electrons
Orbitals are regions in an atom where electrons are most likely to be found. There are three types of p-orbitals: px, py, and pz. Each p-orbital can hold a maximum of two electrons.

- The p-orbitals have a dumbbell shape and are oriented along the x, y, and z axes.
- Each p-orbital can hold a maximum of two electrons. These two electrons have opposite spins, as described by the spin quantum number.
- Therefore, any p-orbital can have a maximum of two electrons.

d) An s-orbital can have a maximum of two electrons
An s-orbital is a spherical-shaped orbital that is closest to the nucleus. It can hold a maximum of two electrons.

- The s-orbital has a spherical symmetry around the nucleus.
- The s-orbital can hold a maximum of two electrons with opposite spins, as described by the spin quantum number.
- Therefore, an s-orbital can have a maximum of two electrons.

In conclusion, all the given statements (a, b, c, and d) are correct.