The correct sequence of quantum numbers (n,l,m) for the electron of the outermost orbit of a chromium atom is:

b) 4,0,0,1/2

Explanation:

1. Quantum Numbers:
Quantum numbers are the values that describe the properties and behavior of electrons in an atom. There are four quantum numbers: principal quantum number (n), azimuthal quantum number (l), magnetic quantum number (m), and spin quantum number (s).

2. Principal Quantum Number (n):
The principal quantum number (n) describes the energy level or shell in which an electron resides. It determines the size and energy of the electron's orbital. The values of n can be any positive integer starting from 1.

3. Azimuthal Quantum Number (l):
The azimuthal quantum number (l) describes the shape of the electron's orbital. It defines the subshell within a given energy level. The values of l can range from 0 to (n-1) for a given value of n.

4. Magnetic Quantum Number (m):
The magnetic quantum number (m) describes the orientation of the orbital in space. It specifies the exact orbital within a subshell. The values of m range from -l to +l, including zero.

5. Spin Quantum Number (s):
The spin quantum number (s) describes the spin state of an electron. It can have two possible values: +1/2 (spin-up) or -1/2 (spin-down).

6. Chromium Atom:
The electron configuration of a chromium atom is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵. Chromium has an atomic number of 24, which means it has 24 electrons. The outermost electron of chromium is located in the 4s orbital.

7. Determining the Quantum Numbers:
To determine the quantum numbers of the electron in the outermost orbit of chromium, we look at the electron configuration.

- The principal quantum number (n) for the outermost electron in the 4s orbital is 4.
- The azimuthal quantum number (l) for an s orbital is 0.
- The magnetic quantum number (m) for an s orbital is 0.
- The spin quantum number (s) can be either +1/2 or -1/2.

8. Correct Sequence:
Based on the above analysis, the correct sequence of quantum numbers for the electron of the outermost orbit of a chromium atom is:

4, 0, 0, 1/2 (option b)

This means that the outermost electron in the chromium atom has a principal quantum number of 4, an azimuthal quantum number of 0 (s orbital), a magnetic quantum number of 0, and a spin quantum number of +1/2.

B