To determine what happens to the inductance when the number of turns of a coil is decreased, let's examine the relationship between inductance and the number of turns.

The inductance of a coil (denoted as \(L\)) is given by the formula:

\(L = \frac{\mu N^2 A}{l}\)

where:

• \(\mu\) is the permeability of the core material.
• \(N\) is the number of turns of the coil.
• \(A\) is the cross-sectional area of the coil.
• \(l\) is the length of the coil.

From this formula, it's clear that the inductance \(L\) is directly proportional to the square of the number of turns, \(N^2\). Therefore, if the number of turns \(N\) is decreased, the inductance \(L\) will decrease.

Let us consider the behavior step-by-step:

1. Understanding the formula: Inductance depends on \(N^2\), meaning changes in the number of turns will have a squared effect on inductance.
2. Decrease in number of turns: Reducing \(N\) means \(N^2\) decreases.
3. Effect on Inductance: The inductance directly decreases if \(N^2\) decreases, because they are proportional.

Thus, the correct answer is: Decrease.