To boil water

[Bellringer]

This may be the wrong spot, but.
Which is the most economical way to boil a quart of water.
An electic kettle or a kettle on a gas stove.

[minesapint]

First of all, the Science category is the best one to place this question without a doubt.

The problem is that as your question stands, it can't be answered for two reasons. The first is that we don't know the wattage of the kettle. Although many electric kettles nowadays have a 3kW "rapid-boil" element, they still make kettles of 1.5kW, 2kW and 2.5kW.

The second reason is that the same applies to a kettle on a gas stove. My last gas stove had burners "rated" at 1kW and 1.5kW. Most stoves have burners of different sizes, so it can't be worked out without this information.

[wildwood]

As far as energy is concerned, I would pick the kettle as on a stove a lot of heat escapes but I don't know how this would work out financially.

[north star]

I agree with wildwood that the kettle would be the most efficient as the energy lost in the heat transfer would be less with the kettle, principally because the element is immersed in the liquid. For the actual financial costs, for the electric kettle you will need a Wattmeter, to measure how much electricity was used and for the gas example, a flowmeter to measure how much gas was used. You will also need your latest utility bills and some maths.