(i) To find the proportion of melons classified as small, we calculate the z-score for 350 grams using the formula:

\(z = \frac{350 - 450}{120} = -0.833\)

The proportion of melons weighing less than 350 grams is given by the cumulative distribution function (CDF) for a standard normal distribution at \(z = -0.833\). From standard normal distribution tables, \(\Phi(-0.833) \approx 0.2025\). Therefore, the proportion of melons classified as small is 20.25%.

(ii) The remaining melons are divided equally between medium and large. The proportion of melons not classified as small is \(1 - 0.2025 = 0.7975\). Half of these are classified as large, so the proportion classified as large is \(0.7975 / 2 = 0.39875\).

We need to find the z-score corresponding to a cumulative probability of \(1 - 0.39875 = 0.60125\). From standard normal distribution tables, \(z \approx 0.257\).

Convert this z-score back to the original scale using:

\(x = 120 \times 0.257 + 450 = 481\)

Thus, the weight above which melons are classified as large is 481 grams.