21.

CH$\equiv$CH $\underset{{\mathrm{H}}_2{\mathrm{SO}}_4}{\overset{{\mathrm{HgSO}}_4}{\to }}$ $\underset{{\mathrm{H}}_2\mathrm{O}}{\overset{{\mathrm{CH}}_3\mathrm{MgBr}}{\to }}$ $\stackrel{\mathrm{P}/{\mathrm{Br}}_2}{\to }$

• CH₃CH(Br)CH₃

• CH₃CH₂CH₂Br

• CH₂=CH-Br

• BrCH=CH-CH₃

Number of bonds in benzene :

• 6$\mathrm{\sigma }$ and 3$\mathrm{\pi }$

• 12$\mathrm{\sigma }$ and 3$\mathrm{\pi }$

• 3$\mathrm{\sigma }$ and 12$\mathrm{\pi }$

• 6$\mathrm{\sigma }$ and 6$\mathrm{\pi }$

(I) and (II) are :

• enantiomers

• diastereomers

• meso compound

• identical

Silicon is :

• semi - conductor

• insulator

• conductor

• none of these

When lead nitrate is heated it produces :

• NO₂

• NO

• N₂O₅

• N₂O

Which of the following is not an actinide ?

• Curium

• Californium

• Uranium

• Terbium

Europium is :

• s - block element

• p - block element

• d - block element

• f - block element

Number of unpaired electrons in Mn⁴⁺ is :

• 3

• 5

• 6

• 4

Which of the following is not hydrolysed ?

• AsCl₃

• PF₃

• SbCl₃

• NF₃

If hydrogen electrode dipped in two-solution of pH = 3 and pH = 6 and salt bridge is connected , the emf of resulting cell is :

• 0.177 V

• 0.3 V

• 0.052 V

• 0.104 V