C

Step 1: Understand the concept of magnetic moment. The magnetic moment of a magnet is given by the product of the pole strength (m) and the distance (l) between the poles:
$$ M = m imes l $$
Step 2: Consider the effect of making a hole at the center of the magnet. The hole will remove some of the material from the magnet but it will not affect the overall pole strength or the distance between the poles since the arrangement remains symmetric.
Step 3: Since neither the pole strength nor the effective length between the poles changes, the magnetic moment remains constant.
Conclusion: Therefore, the magnetic moment of the bar magnet will not change.