The given compounds in decreasing order of acidity is

HBr > HCl > H2O > LiH

Following is the reasoning:
1. The acidic strength of hydrogen halide increases in the order of HF< HCl< HBr< HI. Thus we have HBr > HCl.

2. Then we know that in each horizontal row of the periodic table, the most basic hydrides are on the left and the most acidic hydrides are on the right. . Also, HCl and HF are stronger acids than H2O because Cl- and F- are much weaker bases than OH-. Thus HBr > HCl > H2O.

3. And finally LiH comes towards left on the periodic table and as mentioned it would be most basic hydride. Thus the order comes up to be HBr > HCl > H2O > LiH

I hope you understood!