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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!