Question

Assertion(A) : Borax bead test is applicable only to coloured salt.
Reason(R) : In borax bead test, colured salts are decomposed to give colured metal meta borates.

• A. If both (A) and (R) are true and (R) is the correct explanation of (A)
• B. If both (A) and (R) are true but (R) is not correct explanation of (A)
• C. If (A) is true but (R) is false
• D. If (A) is false and (R) is true

Answer 1

The correct option is A If both (A) and (R) are true and (R) is the correct explanation of (A)

Borax bead test is applicable to only coloured salts. This is based on the fact that coloured cations form metaborates of specific colour. In this test a pinch of borax is taken on platinum wire loop and is heated to get a glassy bead. The bead is touched with a speck of the coloured salt and is heated in oxidising and reducing flame.
$N{a}_2{B}_4{O}_7.10H_{2}O\to N{a}_2{B}_4{O}_7+10H_{2}O$
Borax
$N{a}_2{B}_4{O}_7\to 2NaB{O}_2+B_2{O}_3$
$2NaB{O}_2+B_2{O}_3$ is glassy bead.
The test is further explained in figure.