What is saturation of water vapour pressure?

Look at the picture and explain the reason behind what is happening.

$\left(\mathrm{a}\right)$ ${\mathrm{CuSO}}_4.5{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)\rightleftharpoons {\mathrm{CuSO}}_4.3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)$    ${\mathrm{K}}_{\mathrm{p}}=4\times {10}^{-4} {\mathrm{atm}}^2$

$\left(\mathrm{b}\right)$ ${\mathrm{Na}}_2{\mathrm{SO}}_4.10{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)\rightleftharpoons {\mathrm{Na}}_2{\mathrm{SO}}_4.5{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)+5{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)$    ${\mathrm{K}}_{\mathrm{p}}=2.43\times {10}^{-9} {\mathrm{atm}}^5$

$\left(\mathrm{c}\right)$ ${\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3.5{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)\rightleftharpoons {\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3.2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)$    ${\mathrm{K}}_{\mathrm{p}}=6.4\times {10}^{-5} {\mathrm{atm}}^3$

What is the order of partial pressure of water vapours at equilibrium and relative humidity respectively?

Humidity is calculated by Aneroid Barometer.

Isohel refers to equal sunshine.

Why does warm air hold water Vapour?