An insoluble but wettable particle can still serve as a condensation nucleus because
Answer: A
Wetting allows a film to spread with a much larger radius of curvature than a free cluster of the same volume. Such particles require a higher supersaturation than soluble ones but far less than homogeneous nucleation.
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Consider the following statements about Kohler theory.
1. It combines the curvature and solute effects in one expression.
2. Its maximum defines the critical supersaturation of a particle.
3. It applies only to completely insoluble particles.
Answer: B
The first two are correct and are the substance of the theory. The third inverts its scope, since the solute term is central and an insoluble particle is the limiting case where that term vanishes. What remains in that case is the pure Kelvin curvature expression.
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All of the following are represented in the Kohler equation EXCEPT
Answer: C
Vertical velocity governs how fast supersaturation is supplied, but it does not appear in the equilibrium equation itself. The other three all enter directly through the curvature or the solute term. The equation describes equilibrium, not the dynamics that reach it.
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Assertion (A): The updraught speed influences how many droplets a cloud forms.
Reason (R): A faster ascent produces a higher peak supersaturation and so activates smaller nuclei.
Answer: D
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the chain. A faster updraught cools the parcel faster, so vapour is made available faster than the growing droplets can consume it and the supersaturation peaks higher before the feedback closes it off. A higher peak activates nuclei with higher critical supersaturations, so more and smaller droplets form - which is why a vigorous convective cloud has a very different droplet spectrum from a gently lifted stratus.
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Deliquescence of a soluble aerosol particle is
Answer: A
Correct answer: its spontaneous uptake of water below saturation
A soluble particle takes up water and dissolves into a concentrated solution droplet at a characteristic relative humidity below 100 per cent - about 75 per cent for sodium chloride. Deliquescence is why haze forms well before cloud does, why visibility deteriorates on a humid day, and why a soluble particle is already a droplet by the time the Kohler curve becomes relevant.
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Three of the following describe an activated cloud droplet. Which is the odd one out?
Answer: B
Stable equilibrium with the ambient humidity is the defining property of an unactivated haze droplet. The other three are three ways of stating the same activated condition. Activation is a threshold crossing rather than a gradual transition.
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