JEE Main 2023 · 30 January · morning · Single correct · +4 / −1
Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : In expensive scientific instruments, silica gel is kept in watch-glasses or in semipermeable membrane bags.
Reason (R) : Silica gel adsorbs moisture from air via adsorption, thus protects the instrument from water corrosion (rusting) and / or prevents malfunctioning.
In the light of the above statements, choose the correct answer from the options given below :
- (a) Both (A) and (R) are true and (R) is the correct explanation of (A)
- (b) (A) is true but (R) is false
- (c) (A) is false but (R) is true
- (d) Both (A) and (R) are true but (R) is not the correct explanation of (A)
Answer and solution
Answer (a) Both (A) and (R) are true and (R) is the correct explanation of (A)
Solution
Chemistry ma’am · 4 steps
Silica gel is there for one job: to trap water vapour on its surface before the instrument can.
- Check the Assertion. Packets of silica gel are kept inside the cases of costly instruments, in open watch-glasses or porous bags. This is standard practice, so (A) is true.
- Check the Reason. Silica gel (SiO₂ in a porous form) has a huge surface area. Water vapour from the air sticks to this surface, which is adsorption, so the air around the instrument stays dry. Dry air means less corrosion and fewer faults, so (R) is true.
- Does R explain A. The open watch-glass or porous bag lets moist air reach the gel's surface. The gel is there only to adsorb that moisture, so (R) gives the exact reason for (A).
- So. Both statements are true and (R) correctly explains (A), which is option (a).
The idea to keep. Silica gel and alumina are common adsorbents for moisture. They keep instruments, medicines and food dry. Large surface area is the reason they adsorb so well.
Answer from the NTA final answer key. Solution by PrepWiser.