A solid weighs 1.5kgf in air and 0.9kgf in a liquid of density 1.2×10.3 kgm-3. Calculate relative density of solid.

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.

Both models are effective because they show the valence electrons, and these valence electrons indicate the reactivity of an element.

13) a 14) a15) b16) i don't know sorry17) a (maybe)