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 NH3 =6.022\(\times 10^{23}\) molecules of NH3
and
1 mole of HNO3 =6.022\(\times 10^{23}\) molecules of HNO3
\(\therefore Ratio ={6.022\times 10^{23}\over 6.022\times 10^{23}}\)
therefore , the ratio of molecules of NH3 and HNO3 is 1:1