Which combination cannot be used for the preparation of hydrogen gas in the laboratory?
$\mathrm{I}.$ Zinc/conc. ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$
$\mathrm{I}\mathrm{I}.$ Zinc/dil. $\mathrm{H}\mathrm{N}{\mathrm{O}}_3$
$\mathrm{I}\mathrm{I}\mathrm{I}.$ Pure Zinc/dil. ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$

• A

  I and II
• Correct answer
  B

  I, II and III
• C

  III only
• D

  I and III

Hence, the correct answer is option: 'B'.