JEE Main 2021 · 31 August · evening · Single correct · +4 / −1
Match List - I with List - II
Choose the most appropriate answer from the options given below :
| List - I (Parmeter) | List - II (Unit) | ||
|---|---|---|---|
| (a) | Cell constant | (i) | S cm²mol⁻¹ |
| (b) | Molar conductivity | (ii) | Dimensionless |
| (c) | Conductivity | (iii) | m⁻¹ |
| (d) | Degree of dissociation of electrolyte | (iv) | Ω ⁻¹m⁻¹ |
- (a) (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)
- (b) (a)-(iii), (b)-(i), (c)-(ii), (d)-(iv)
- (c) (a)-(i), (b)-(iv), (c)-(iii), (d)-(ii)
- (d) (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
Answer and solution
Answer (a) (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)
Solution
Chemistry ma’am · 4 steps
Build each unit from its defining formula, and the matching sorts itself out.
- Cell constant. Cell constant is G^* = l/A, a length divided by an area. Its unit is m/m² = m⁻¹, so (a) goes with (iii).
- Conductivity. Conductivity is κ = 1/ρ, and resistivity ρ has the unit Ω m. So κ has the unit Ω⁻¹ m⁻¹, and (c) goes with (iv).
Λₘ = κ/c ⇒ (S cm⁻¹)/(mol cm⁻³) = S cm² mol⁻¹
- Molar conductivity. Dividing conductivity by molar concentration gives S cm² mol⁻¹, so (b) goes with (i). Degree of dissociation α = Λₘ/Λₘ° is a ratio of two identical units, so it is dimensionless, and (d) goes with (ii).
- So. The matching is (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii), which is option (a).
The idea to keep. Never memorise conductance units blindly. Write the defining formula, put in the units, and cancel: l/A, 1/ρ, κ/c and Λₘ/Λₘ° give every answer.
Answer from the NTA final answer key. Solution by PrepWiser.