The element which can form an acidic oxide should be the one whose atomic number is :

(a) 6 (b) 16 (c) 12 (d) 19

(b) 16.
The element which can form an acidic oxide should be the one with atomic number 16. Sulphur has an atomic number of 16 and sulphur oxide is acidic.

Note: Option (a) 6: carbon also forms an acidic oxide but the acidic strength of the oxides of sulphur (16) is greater than that of carbon (6).