Question

Example of trivalent acidic radical

Answer 1

HCl, Cl-, HNO3, NO2. this is the answer of your question. 

Answer 2

Hey mate

radical means ION
and
trivalent means one which has VALENCY = 3

acidic radical means negative ion or ANION

So

example will be...
${po4}^{3 - }$
Thanks