How many of the following species are paramagnetic? sc3 + br - mg2 + se?

One: Selenium is Paramagnetic

Explanation:

Those compounds which have unpaired electrons are attracted towards magnet. This property is called as paramagnetism. Lets see why remaining are not paramagnetic.

Electronic configuration of Scandium;

Sc = 21 = 1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹

Sc³⁺ = 1s², 2s², 2p⁶, 3s², 3p⁶

Hence in Sc³⁺ there is no unpaired electron.

Electronic configuration of Bromine;

Br = 35 = 1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁵

Br⁻ = 1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁶

Hence in Br⁻ there is no unpaired electron.

Electronic configuration of Magnesium;

Mg = 12 = 1s², 2s², 2p⁶, 3s²

Mg²⁺ = 1s², 2s², 2p⁶

Hence in Mg²⁺ there is no unpaired electron.

Electronic configuration of selenium;

Se = 34 = 1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁴

Or,

Se = 34 = 1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4px², 4py¹, 4pz¹

Hence in Se there are two unpaired electrons hence it is paramagnetic in nature.