The electrons fill energy levels from the lowest available energy level, based of three typical rules.
1) Follow Aufbau rule: fill from lower to higher energy levels (1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p)
2) Pauly exclusion principle: two electrons can not have the same four quantum numbers
3) Hund rule: if the orbitals have the same energy, the electrons must go to different orbitals before two occupies the same orbital.
When you pack down snow into ice the snow hardens and some times turns into an icicle
Yes! Exposure to formaldehyde even once can irritate the eyes and respiratory tract.
D. Heating with a flame, as this would provide thermal energy to the solution/substance
There’s 4 atoms in Hydrogen, 4 atoms in Nitrogen and 12 atoms in Oxygen so 20 (Hope this is right!)
