Which of the following compounds contain(s) no covalent bond(s) ? <br> $KCl, \; PH_3,\; O_2, \; B_2H_6, \;H_2SO_4$

Question

( A ) $KCl,\; B_2H_6,\; PH_3$
( B ) $KCl, \; H_2SO_4$
( C ) $KCl,\;B_2H_6$
( D ) $KCl$