(a) Treatment of Foreign Currency Transactions:

According to IAS 21, foreign currency transactions must be recorded using the exchange rate at the date of the transaction. The treatment of foreign currency transactions involves:

1. Initial Recognition: At the date of the transaction, the foreign currency amount is translated into the functional currency using the spot exchange rate. Any gain or loss that arises at this point is not recognized until the transaction settles.
2. Subsequent Measurement: At the reporting date, any monetary items denominated in a foreign currency must be translated using the closing exchange rate. This retranslation will result in foreign exchange gains or losses, which must be recognized in profit or loss for the period.
3. Non-Monetary Items: For non-monetary items, such as property, plant, and equipment, the exchange rate used at the time of acquisition remains unless there is an impairment.
4. Recognition of Exchange Differences: Any exchange differences resulting from the settlement of a monetary item or from translating monetary items at the closing rate must be recognized in profit or loss.

(b) Accounting for Investment Property in (i):

For the investment property acquired for $1,000,000, the accounting treatment as of April 30, 2018, would involve:

1. Initial Measurement: The investment property would be initially recognized at its cost, translated into Naira using the exchange rate on the acquisition date.
2. Fair Value Model: As the company uses the fair value model, the investment property would be remeasured at its fair value of $1,200,000 at the reporting date. The exchange rate at this date will be used for translating the fair value into Naira.
3. Recognition of Exchange Difference: Any gain or loss due to changes in the exchange rate and the fair value adjustments should be recognized in profit or loss.

(c) Accounting for the Wholly Owned Subsidiary in (ii):

The accounting treatment for the acquisition of a wholly owned subsidiary with a goodwill of $400,000 includes:

1. Initial Recognition of Goodwill: Goodwill is recognized as the excess of the purchase consideration over the fair value of the identifiable net assets at the acquisition date. It should be translated into Naira using the spot exchange rate on the date of acquisition.
2. Subsequent Measurement: Goodwill must be tested for impairment annually or whenever there are indicators of impairment, in accordance with IAS 36.
3. Translation at Year-End: Any adjustments arising from the translation of the goodwill into Naira must be recognized in OCI, given that goodwill is considered a non-monetary item.