We know, Impulse of a body is change in momentum.
Also, the final velocity of wood block is 0 m/s.
So, Impulse = Final Momentum - Initial Momentum
Impulse = 0 - ( 0.05 kg × 350 m/s )
Impulse = - 17.5 kg m/s
Therefore, the impulse exerted by the wood on the bullet is -17.5 kg m/s .