Correct answer is 1:1
one mole of any substance,compound , or elements contain particles equal to avagadro's number i.e. 6.022\(\times 10^{23}\)
\(\therefore \) 1 mole of NH_{3} =6.022\(\times 10^{23}\) molecules of NH_{3}
and
1 mole of HNO_{3} =6.022\(\times 10^{23}\) molecules of HNO_{3}
\(\therefore Ratio ={6.022\times 10^{23}\over 6.022\times 10^{23}}\)
therefore , the ratio of molecules of NH_{3} and HNO_{3} is 1:1