Scuba divers must cope with high concentrations of dissolved gases while breathing air at high pressure, underwater. Increased pressure increases the solubility of atmospheric gases in blood. When divers come towards surface, the pressure gradually decreases. This blocks capillaries and creates a medical condition called bends. To avoid bends, the tanks are used by scuba divers that are filled with air diluted with helium $(11.7 \%$ helium, $56.2 \%$ nitrogen and $32.1 \%$ oxygen). Thus, option (d) is correct.