$(a)$ Explain the following phenomena with the help of Henry’s law.
$(i)$ Painful condition known as bends.
$(ii)$ Feeling of weakness and discomfort in breathing at high altitude.
$(b)$ Why does a soda water bottle kept at room temperature fizz on opening?

(N/A) $(i)$ According to Henry's law,the partial pressure of a gas is directly proportional to its solubility in a liquid. Scuba divers,when ascending towards the surface,experience a gradual decrease in external pressure. This reduction in pressure causes the dissolved gases (mainly $N_2$) in the blood to become less soluble,leading to the formation of nitrogen bubbles in the bloodstream. These bubbles block capillaries and create a painful and dangerous medical condition known as bends.
$(ii)$ At high altitudes,the partial pressure of oxygen is significantly lower than at ground level. According to Henry's law,this lower partial pressure results in lower concentrations of oxygen dissolved in the blood and tissues of individuals. This low blood oxygen level leads to symptoms of weakness and discomfort in breathing,often referred to as anoxia.
$(b)$ When a soda water bottle is opened,the partial pressure of $CO_2$ above the liquid decreases suddenly. As per Henry's law,the solubility of $CO_2$ decreases with a decrease in pressure,causing the dissolved $CO_2$ to escape rapidly in the form of bubbles,which produces a fizzing sound.