Class 12 NEET Chemistry Solutions Questions

(A) To calculate molality, we use the formula:
‌Molality‌=‌

‌moles of solute‌

‌mass of solvent (in kg)‌

Moles of ethanoic acid =‌

2.5

60

and mass of benzene =75‌ g‌=0.075‌ kg‌.
So, ‌Molality‌=‌

2.5∕60

0.075

=0.556‌‌molal‌
Therefore, statement (A) is correct.
(B) To calculate molarity, we use the formula:
‌Molarity‌=‌

‌moles of solute‌

‌volume of solution (in L)‌

Moles of NaOH =‌

5

40

and volume =450‌ mL‌=0.45‌ L‌.
So, ‌Molarity‌=‌

5∕40

0.45

=0.278‌‌M‌
Hence, statement (B) is also correct.
(C) Aquatic animals find cold water more suitable because the solubility of gases increases when temperature decreases. From Henry’s law:
KH∝‌Temperature‌‌‌‌and‌‌‌KH∝‌

1

‌Solubility‌

This means higher temperature reduces gas solubility. So, statement (C) is correct.
(D) According to Henry’s law, the relationship between pressure and solubility is given by:
P=KHX
Here, P∝X, i.e., solubility increases with an increase in pressure. So, the statement “solubility decreases with pressure” is incorrect.
(E) The mole fraction of component B in a binary mixture is given by:
xB=‌

nB

nA+nB

The given statement uses nA in the numerator, which is wrong. Hence, (E) is incorrect.