Identify the correct statements about alkali metals.
A. The order of standard reduction potential () for alkali metal ions is .
B. CsI is highly soluble in water.
C. Lithium carbonate is highly stable to heat.
D. Potassium dissolved in concentrated liquid ammonia is blue in colour and paramagnetic.
E. All the alkali metal hydrides are ionic solids.
Choose the correct answer from the options given below:
A. The order of standard reduction potential () for alkali metal ions is .
B. CsI is highly soluble in water.
C. Lithium carbonate is highly stable to heat.
D. Potassium dissolved in concentrated liquid ammonia is blue in colour and paramagnetic.
E. All the alkali metal hydrides are ionic solids.
Choose the correct answer from the options given below:
- A.C and E only
- B.A, B, D only
- C.A, B and E only
- D.A and E only
Show answer and solution
Correct option: D
Solution
The two correct statements are A and E.
Statement A: The standard reduction potential order is Na > Rb > Li. Although it seems counterintuitive, Li has the most negative reduction potential (strongest reducing agent) due to its exceptionally high hydration enthalpy, which makes it harder to reduce Li⁺ back to Li. Rb sits between Na and Li in this ordering, so Na > Rb > Li is correct.
Statement E: All alkali metal hydrides (LiH, NaH, KH, RbH, CsH) are ionic solids containing H⁻ ions. This is true — unlike transition metal hydrides, alkali metal hydrides are purely ionic in nature.
The other statements are wrong: CsI is sparingly soluble (large cation + large anion, low hydration); Li₂CO₃ is thermally unstable among alkali carbonates (Li⁺ high charge density polarises CO₃²⁻, causing decomposition); and potassium dissolved in liquid ammonia gives a blue, diamagnetic (not paramagnetic) solution because the solvated electrons pair up at higher metal concentrations (bronze/blue color, but the solution is actually diamagnetic in concentrated form).
Statement A: The standard reduction potential order is Na > Rb > Li. Although it seems counterintuitive, Li has the most negative reduction potential (strongest reducing agent) due to its exceptionally high hydration enthalpy, which makes it harder to reduce Li⁺ back to Li. Rb sits between Na and Li in this ordering, so Na > Rb > Li is correct.
Statement E: All alkali metal hydrides (LiH, NaH, KH, RbH, CsH) are ionic solids containing H⁻ ions. This is true — unlike transition metal hydrides, alkali metal hydrides are purely ionic in nature.
The other statements are wrong: CsI is sparingly soluble (large cation + large anion, low hydration); Li₂CO₃ is thermally unstable among alkali carbonates (Li⁺ high charge density polarises CO₃²⁻, causing decomposition); and potassium dissolved in liquid ammonia gives a blue, diamagnetic (not paramagnetic) solution because the solvated electrons pair up at higher metal concentrations (bronze/blue color, but the solution is actually diamagnetic in concentrated form).
[JEE Main 2023 · 24 Jan · Shift 2]