NEET Practice Questions (MCQs) with Answers & Solutions

(d)

                  $$\begin{gathered} {\mathrm{B}}_2{\mathrm{O}}_3\underset{∆}{\overset{\mathrm{Al}}{\to }}\mathrm{B} \left(\mathrm{crystalline}\right) \\ {\mathrm{B}}_2{\mathrm{O}}_3\underset{∆}{\overset{\mathrm{Mg}}{\to }} \left(\mathrm{Amorphous}\right) \end{gathered}$$

(c) $\mathrm{Al}(\mathrm{OH}{)}_3$ dissolves in $\mathrm{NaOH}$ solution to give $\mathrm{Al}(\mathrm{OH}{)}_4^{‐}$ ion which is supposed to have the

       octahedral complex species $\mathrm{Al}(\mathrm{OH}{)}_3+\mathrm{NaOH}(\mathrm{aq}\left)\underset{}{\to }{\left[\mathrm{Al}{\left(\mathrm{OH}\right)}_4{\left({\mathrm{H}}_2\mathrm{O}\right)}_2\right]}^{-}\right(\mathrm{aq})+{\mathrm{Na}}^{+}(\mathrm{aq})$

Borax (Na2B4O7.10H2O) is a hydrated sodium tetraborate containing two BO3³⁻ and two BO4⁵⁻ units. It contains 6 B-O-B bonds, not 4. The other statements about borax being a primary standard, buffer solution, and its structural units are correct.

(a)     ${\mathrm{H}}_3{\mathrm{BO}}_3$ acts are weak monobasic Lewis acid.

         (i) $\mathrm{B}(\mathrm{OH}{)}_3+\mathrm{NaOH}\underset{}{\to }\mathrm{Na}\left[\mathrm{B}{\left(\mathrm{OH}\right)}_4\right]$

         On addition of cis 1, 2 diol in ${\mathrm{H}}_3{\mathrm{BO}}_3$ solution, acidic strength of ${\mathrm{H}}_3{\mathrm{BO}}_3$

          increase due to chelation effect.

(c)     ${\mathrm{Ag}}^{+}$ ion can not give borax bead test because formed silver metaborate

         ${\mathrm{AgBO}}_2$ is white/colourless.

(d) ${\mathrm{BF}}_3+{\mathrm{LiAlH}}_4\stackrel{\mathrm{Ether}}{\to }{\mathrm{B}}_2{\mathrm{H}}_6+\mathrm{LiF}+{\mathrm{AlF}}_3$

     ${\mathrm{NH}}_3$ can react with ${\mathrm{B}}_2{\mathrm{H}}_6$

     ${\mathrm{B}}_2{\mathrm{H}}_6+2{\mathrm{NH}}_3\stackrel{\mathrm{warm}}{\to }{\left[{\mathrm{BH}}_2.2{\mathrm{NH}}_3\right]}^{+}.{\left[{\mathrm{BH}}_4\right]}^{-}\stackrel{200°\mathrm{C}}{\to }{\mathrm{B}}_3{\mathrm{N}}_3{\mathrm{H}}_6$ (Inorganic benzene)

The amphibole silicate structure has 2.5 corner-shared tetrahedral per tetrahedron. This is because the silicon-oxygen tetrahedra share two corners with neighboring tetrahedra and one unshared corner or 'bridging oxygen' with another tetrahedron.

(d) (i) Pyro silicates : (1 corner O-atom per tetrahedron is shared)

      (ii) Cyclic silicates : (2 corner O-atom per tetrahedron is shared)

      (iii) Double chain silicate (One unit shares two corner O-atom while one unit shares three corner

            O-atom)

       (iv) Single chain sillicate : (2 corner O-atom are shared) 

       (v) 3D silicate : (4 corner O-atom are shared)

       (vi) Sheet silicates : (3 corner O-atom are shared)