Q4. Assertion: using NCERT’s oxygen constants, water at 293 K holds more dissolved oxygen than water at 303 K at the same oxygen partial pressure. Reason: the Henry’s law constant of oxygen increases with temperature. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion for these stated conditions: the larger KH at 303 K means less dissolved oxygen. NCERT draws the lesson that aquatic species are more comfortable in cold waters (page 8); that does not mean every aquatic animal prefers colder water (reasoned).
Q5. Find the mole fraction of CO2 dissolved in water at 298 K under a CO2 partial pressure of 1 bar (KH = 1.67 kbar).
x = p/KH = 1/1670 = 6.0 × 10−4 (KH from NCERT Table 1.2, page 8).
Q6. Solute particles keep dissolving in a saturated solution, yet its concentration does not change. Why?
Crystallisation goes on at the same rate as dissolution: the two are in dynamic equilibrium (NCERT page 6).
Q7. At constant temperature, the partial pressure of a gas above its solution is doubled. What happens to its mole fraction in the solution?
It doubles, since x = p/KH with KH fixed at that temperature (NCERT Eq. (1.11), page 7).
Q8. Why do divers who come up too fast from a deep dive suffer from the bends?
At depth the high pressure dissolves more nitrogen in the blood; as the pressure falls, bubbles can form in blood and tissues and cause decompression sickness; the process depends on exposure and decompression, not pressure alone (NCERT page 8).