At one place on earth, the resultant magnetic field is 0.25 G and the angle of dip is 45°. The horizontal component of earth's magnetic field will be

0.18 G

The correct answer is Option (1) → 0.18 G

Given:

Resultant magnetic field: $B = 0.25$ G

Angle of dip: $\delta = 45^\circ$

Horizontal component: $B_H = B \cos \delta$

$B_H = 0.25 \cos 45^\circ = 0.25 \times \frac{1}{\sqrt{2}} \approx 0.177$ G

Answer: $B_H \approx 0.177$ G