A projectile is projected with velocity of \( 25 \, \text{m/s} \) at an angle \( \theta \) with the horizontal. After \( t \) seconds its inclination with horizontal becomes zero. If \( R \) represents horizontal range of the projectile, the value of \( \theta \) will be: [use \( g = 10 \, \text{m/s}^{2} \)]