Calculate the energy of a photon having wavelength $250nm.($speed of light $=3{10}^8\frac{m}{s},$ planck's constant $=6\mathrm{.}6{10}^{-34}J.S)$

Write the electron configuration of the following atoms$/$ions according to aufbau principle

a$.$ potassium

b$.$ Chloride ion

c$.$ magnesium ion

Complete the following table.

$\backslash$table$[[$Particle$,\backslash$table$[[$Mass$],[$number$]],\backslash$table$[[$Atomic$],[$Number$]],$Protons,Electrons,Neutrons$],{[}_{35}Br,,,,,],{[}_{137},,,,,],{[}_{56}B{a}^{2+},,,,,],{[}_{52}28,,,,,]]$

Identify the following elements

a$)$ Contains $3$ electrons in $3p$ subshell.

b$)$ Valence electron configuration is $5s^2$

c$)$ Contains three electrons in the fourth energy leve

d$)$ Has a complete second energy level.

e$)$ Contains two unpaired electrons in its third energy level.