Which of the following compounds contain(s) no covalent bond(s)?

$\mathrm{KCl},\mathrm{ }{\mathrm{PH}}_3,\mathrm{ }{\mathrm{O}}_2,\mathrm{ }{\mathrm{B}}_2{\mathrm{H}}_6,\mathrm{ }{\mathrm{H}}_2{\mathrm{SO}}_4$

• A

  $\mathrm{KCl},\mathrm{ }{\mathrm{B}}_2{\mathrm{H}}_6$
• B

  $\mathrm{KCl},\mathrm{ }{\mathrm{B}}_2{\mathrm{H}}_6,\mathrm{ }{\mathrm{PH}}_3$
• C

  $\mathrm{KCl},\mathrm{ }{\mathrm{H}}_2{\mathrm{SO}}_4$
• Correct answer
  D

  $\mathrm{KCl}$

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