Amount of Niobium-91 initially
= 300/91 =3.2967mol
2040 years = 3 ×680 = 3 half-lives
therefore, amount left = 0.4121mol
mass of Niobium-91 remaining = 0.4121 ×91 =37.5g
1. option B
2. ground state Fe : [Ar] 4s² 3d⁶
<h3>
Further explanation</h3>
Aufbau rule
<em>Electrons occupy orbitals of the lowest energy level</em>
Charging electrons in the sub-shell uses the following sequence:
1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁶, 5s², 4d¹⁰, 5p⁶, 6s², etc.
So the correct choice of answer is B.
Ground state is the state of electrons filling skins with the lowest energy levels.
Excited state is the state of electrons which occupy a higher energy level
The atomic number of Fe = 26, so electrons=26
Ground state configuration of Fe : [Ar] 4s² 3d⁶ or
1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d⁶
A chemical property is a characteristic of a substance that may be observed when it participates in a chemical reaction. Examples of chemical properties include flammability, toxicity, chemical stability, and heat of combustion
