Pick out the statement which is not relevant in the discussion of colloids

Options

A. Sodium aluminium silicate is used in the softening of hard water
B. Potash alum is used in shaving and as a antiseptic in medicine
C. Artificial rain is caused by throwing electrified sand on the clouds from an aeroplane
D. Deltas are formed at a place where the river pours its water into the sea

Explanation

To solve the question of identifying the statement that is not relevant in the discussion of colloids, we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding Colloids**:
- Colloids are mixtures where very small particles of one substance are dispersed within another substance. These particles are typically in the range of 1 nanometer to 1 micrometer in size. Examples include gels, sols, and emulsions.

2. **Analyzing Each Option**:
...