Question

Which of the following statement(s) is(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, caesium is the most reactive
• D. The reducing character of the alkali metal hydribes follow the order: $LiH>NaH>KH>RbH>CsH$

Answer 1

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

The correct options are
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, caesium is the most reactive

An alkali metal salts impart a characteristic colour to the Bunsen flame due to low ionization enthalpy. When the metal is brought in contact with the flame the single electron present in the outermost shell goes to the excited level whose energy falls in the visible range and thus colour is imparted.

Among $LiOH,CsOH,RbOH,CsOH$ and $KOH$, $CsOH$ has the highest solubility in water due to the low lattice enthalpy.

Among the alkali metals, $Cs$ is the most reactive due to its bigger size, the outermost electron is easily available for donation hence low ionization energy.

Hence, the correct options are $A$, $B$ and $C$