Give the decreasing order of acidic strength of the following :
(a) `CH_4`
(b) `H_2 O`
( c) `HF`
(d) `NH_3`
( e) `LiH`
(f) `BeH_2`.

Explanation

To determine the decreasing order of acidic strength for the given compounds, we need to analyze the stability of their conjugate bases. The acidic strength of a compound is influenced by the stability of the conjugate base formed after the compound donates a proton (H⁺). The more stable the conjugate base, the stronger the acid.

### Step-by-Step Solution:

1. **Identify the Compounds and Their Conjugate Bases:**
- (a) **CH₄** → Conjugate base: CH₃⁻
- (b) **H₂O** → Conjugate base: OH⁻
- (c) **HF** → Conjugate base: F⁻
...