How much does a full fare plus a transfer on the rail system using a Ventra Card cost?

The correct answer reflects the current fare structure for using a Ventra Card on the Chicago Transit Authority (CTA) rail system. A full fare on the rail service is $2.50, and this fare includes a transfer. When passengers use a Ventra Card to pay for their trip, they benefit from the integrated pricing model that allows for easy transfers between different modes of transportation within the CTA system.

The cost is structured this way to encourage the use of transfers, making it more convenient and economical for passengers who may need to switch from the rail service to a bus or vice versa on the same journey. Therefore, $2.50 represents the total amount charged for a full fare plus a transfer when utilizing a Ventra Card, making it the correct answer in this scenario.