Tetra-alkyl ammonium salts are called ____salts.

Explanation

**Step-by-Step Solution:**

1. **Understanding Tetra-alkyl Ammonium Salts:**
Tetra-alkyl ammonium salts are formed when a nitrogen atom is bonded to four alkyl groups. This results in a positively charged nitrogen atom because it has four bonds and no lone pairs.

2. **Formation of Tetra-alkyl Ammonium Salts:**
The formation of these salts typically involves the reaction of a tertiary amine with an alkyl halide. The nitrogen atom acts as a nucleophile, attacking the alkyl halide and forming a new bond while displacing the halide ion.

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