Question

Which of the following statements are true about the alkali metals?

• A. All alkali-metal salts impart a characteristic colour to the Bunsen flame.
• B. Among LiOH, CsOH, KOH, and RbOH, CsOH has the highest solubility in water.
• C. Among the alkali metals, cesium is the most reactive.
• D. The reducing character of the alkali metal hydrides follow the order: $LiH>NaH>KH>RbH>CsH$.

Answer 1

Answer: (A), (B), (C)

All alkali-metal salts impart a characteristic colour to the Bunsen flame.
Among LiOH, CsOH, KOH, and RbOH, CsOH has the highest solubility in water.
Among the alkali metals, cesium is the most reactive.

(A) This is because the heat from the flame excites the outermost orbital electron to a higher energy level. When the excited electron comes back to the ground state, there is an emission of radiation in the visible region as given below :

Metal $Li$ $Na$ $K$ $Rb$ $Cs$

Colour Crimson red Yellow Violet/Lilac Red violet Blue.

(B) Down the group the change in lattice energy is more than that of hydration energy.

(C) Because of low ionization energy and melting point.

(D) Reducing nature increases down the group as their stability decreases down the group $CaH>RbH>KH>NaH>LiH.$
Hence, option A, B and C are correct.