C

Step 1: The given trajectory equation is:
$$ y = x - \frac{g}{2u^2} x^2 $$
The term for gravity $g = 10 \text{ m/s}^2$ indicates that this is a projectile motion equation.

Step 2: From this equation, we can identify that the vertical motion is influenced by the acceleration due to gravity. The general form for projectile motion is given by:
$$ y = x \tan(\theta) - \frac{g}{2u^2 \cos^2(\theta)} x^2 $$
By comparing, we can conclude that $\tan(\theta) = 1$ (coefficient of $x$ term), which gives us the angle of projection:
$$ \theta = 45^\circ $$

Step 3: Let's analyze the angle of projection for (i): Looking at the table, option [C] is 45º.
Therefore, the correct answer for (i) matches [C].