Arrange alkali metal fluorides and halides in the decreasing order of solubility.

Explanation

To arrange alkali metal fluorides and halides in decreasing order of solubility, we need to understand the behavior of alkali metals and their compounds with halogens.

### Step-by-Step Solution:

1. **Identify Alkali Metals**: The alkali metals are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). Their reactivity with halogens increases down the group due to decreasing ionization enthalpy and increasing electropositivity.

2. **Order of Alkali Metal Fluorides**:
- The solubility of alkali metal fluorides generally decreases down the group.
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