>The decreasing order of acid strength of the following compounds:  
>
>The given compounds are   
Water ($\ce{H2O}$)  
Ammonia ($\ce{NH3}$)  
Acetylene ($\ce{C2H2}$)  
Triphenyl system ($\ce{Ph3CH}$) 
>
>a) $\ce{NH3}$ > $\ce{Ph3CH}$ > $\ce{C2H2}$ > $\ce{H2O}$  
b) $\ce{H2O}$ > $\ce{C2H2}$ > $\ce{Ph3CH}$ > $\ce{NH3}$  
c) $\ce{C2H2}$ > $\ce{H2O}$ > $\ce{Ph3CH}$  > $\ce{NH3}$   
d) $\ce{Ph3CH}$ > $\ce{C2H2}$ > $\ce{H2O}$ > $\ce{NH3}$  

I gave the answer to be $\ce{Ph3CH}$ > Acetylene > Water > $\ce{NH3}$. Here I have marked the triphenyl system as the most acidic because it has resonance stabilization involved and $\ce{NH3}$ as the least acidic because it has basic nature. Using these two facts I have marked the answer as above however it was wrong. What is the correct order and why?