Which is insoluble in water

Options

A. `H_(2)S`
B. `HgCl_(2)`
C. `Ca(NO_(3))_(2)`
D. `CaF_(2)`

Explanation

To determine which compound is insoluble in water, we need to analyze the solubility of the given compounds based on their polarity and lattice energy. Here’s a step-by-step solution:

### Step 1: Understand Polarity
- Water (H2O) is a polar solvent. For a compound to be soluble in water, it generally needs to be polar as well.

### Step 2: Analyze H2S
- Hydrogen sulfide (H2S) is slightly polar.
- It is known to be slightly soluble in water due to its polarity, but not highly soluble.

### Step 3: Analyze HgCl2
- Mercury(II) chloride (HgCl2) is also polar.
- It is soluble in water, which means it can interact favorably with water molecules.

### Step 4: Analyze CaF2
- Calcium fluoride (CaF2) is an ionic compound.
- It has a very high lattice energy due to the strong electrostatic forces between the calcium ions (Ca²⁺) and fluoride ions (F⁻).

### Step 5: Lattice Energy Consideration
- Compounds with high lattice energy are generally less soluble in water.
- The high lattice energy of CaF2 means that it is not easily dissociated in water, leading to its insolubility.

### Conclusion
- Based on the analysis, the compound that is insoluble in water is **CaF2** (Calcium fluoride).