Which of the following compounds contain(s) no covalent bond(s)<br>$$\text{KCl}$$, $$\text{PH}_3$$, $$\text{O}_2$$, $$\text{B}_2\text{H}_6$$, $$\text{H}_2\text{SO}_4$$

A

$$\text{KCl}$$

B

$$\text{KCl}$$; $$\text{B}_2\text{H}_6$$

C

$$\text{KCl}$$; $$\text{B}_2\text{H}_6$$; $$\text{PH}_3$$

D

$$\text{KCl}$$; $$\text{H}_2\text{SO}_4$$