B

In case (i), since the cart is moving with a constant velocity, the stone projected vertically upwards retains the horizontal velocity of the cart and will fall back into the cart.
In case (ii), the cart is sliding down an incline, which introduces an acceleration component along the incline. The stone, when projected perpendicular to the incline, will not have the same horizontal acceleration and therefore will not fall back into the cart.
Therefore, the stone will only fall back into the cart in case (i).