State which of the following meets the definition of 'revenue' under IAS 18 for Company Z, a retailer of toys. Give reasons for your answer:
1. Sales tax collected on behalf of the taxing authority.
2. Gain on the sale of an investment property.
3. Amounts receivable from customers who have purchased toys.
4. Gain on the sale of equity securities held as investments.
5. Revaluation increment on the revaluation of operating properties under IAS 16.