Chemistry - Complete Pblock- Question with Solution | TestHub

Borax ($N{a}_2{B}_4{O}_7\cdot 10H_{2}O$) upon heating ($\Delta$) first loses water to form anhydrous borax (X). Further strong heating (high T, $\Delta$) decomposes it into sodium metaborate ($NaB{O}_2$) and boric anhydride ($B_2{O}_3$), which is a glassy mass (Y). When Y is heated with CoO, it forms cobalt metaborate ($Co(B{O}_2{)}_2$) which is Z.

The reaction sequence is:

$N{a}_2{B}_4{O}_7\cdot 10H_{2}O\stackrel{\Delta }{\to }N{a}_2{B}_4{O}_7(X)+10H_{2}O$

$N{a}_2{B}_4{O}_7\stackrel{highT}{\to }2NaB{O}_2+B_2{O}_3(Y)$

$B_2{O}_3+CoO\stackrel{\Delta }{\to }Co(B{O}_2{)}_2(Z)$

Cobalt metaborate ($Co(B{O}_2{)}_2$) gives a blue color in both oxidizing and reducing flames due to the formation of cobalt(II) borate glass.

Therefore, the color obtained in reducing and oxidizing flame is blue and blue, respectively.

The final answer is A