WBJEE PYQs for Haloalkanes and Haloarenes with Solutions: Practice WBJEE Previous Year Questions

1.

In which of the reactions given below does H2PO4^- behave as an acid?(i) $H_{3}P{O}_4+H_{2}O\to H_3{O}^{+}+H_{2}P{O}_4^{-}$(ii) $H_{2}P{O}_4^{-}+H_{2}O\to H_3{O}^{+}+HP{O}_4^{2-}$(iii) $H_{2}P{O}_4^{-}+O{H}^{-}\to H_{3}P{O}_4+O^{2-}$

• (A) (i) and (ii)
  
• (B) Only (ii)
  
• (C) Only (i)
  
• (D) Only (iii)
  

2.

Under identical conditions, the $S_N1$ reaction will occur most efficiently with

• tert-butyl chloride
• 1-chlorobutane
• 2-methyl-1-chloropropane
• 2-chlorobutane

3.

Treatment of with $NaNH_2/li \,NH_3$ gives

4.

Na₂CO₃ is prepared by Solvay process but K₂CO₃ can not be prepared by the same because

• K₂CO₃ is highly soluble in H₂O
• KHCO₃ is slightly soluble
• KHCO₃ is appreciably soluble 
• KHCO₃ decomposes

5.

In a mixture, two enantiomers are found to be present in $85\%$ and $15\%$ respectively. The enantiomeric excess $(e, e)$ is

• $85\%$
• $15\%$
• $70\%$
• $60\%$

6.

The ease of dehydrohalogenation of alkyl halide with alcoholic $KOH$ is

• $3^{o} < 2^{o} < 1^{o}$
• $3^{o} > 2^{o} >1^{o}$
• $3^{o} < 2^{o} > 1^{o}$
• $3^{o} > 2^{o} < 1^{o}$

7.

0.400 g of impure CaSO4 (Molar mass = 136) solution when treated with excess of barium chloride solution, gave 0.617 g of anhydrous BaSO4 (Molar mass = 233). The percentage of CaSO4 present in the sample is

• (A) 80.0%
  
• (B) 90.0%
  
• (C) 95.0%
  
• (D) 75.0%