Among the electrolytes Na$$_2$$SO$$_4$$, CaCl$$_2$$, Al$$_2$$(SO$$_4$$)$$_3$$ and NH$$_4$$Cl, the most effective coagulating agent for Sb$$_2$$S$$_3$$ sol is

The Henry's law constant for the solubility of N$$_2$$ gas in water at 298 K is 1.0 $$\times$$ 10$$^5$$ atm. The mole fraction of N$$_2$$ in air is 0.8. The number of moles of N$$_2$$ from air dissolved in 10 moles of water at 298 K and 5 atm pressure is

The reaction of P$$_4$$ with X leads selectively to P$$_4$$O$$_6$$. The X is

The correct acidity order of the following is