[ElectroMaster88]

So today in chemistry class, we learnt about covalent bonds.
There were some questions about the topic, and there was some weird question...
The question was "Which of the following compounds are possible? Explain", and under the question there were drawings of some molecules: Methenium, Hydrogen peroxide, Methylamine, Fluoronium and Fluoromethane.
But for some reason, the teacher said that Methenium and Fluoronium are impossible.
I have tried to search more on the internet, and I can guess that they are "impossible" because Methenium and Fluoronium are ions, and it was not the topic of the lesson...
Can someone help me understand it?

[Babcock_Hall]

Your interpretation is a reasonable one, but perhaps there is more information.  Can you provide representations of the structures of either of them? 

[ElectroMaster88]

Yes this is the picture.
White - Hydrogen
Red - Oxygen
Black - Carbon
Blue - Nitrogen
Green - Fluorine

[Babcock_Hall]

With respect to the compound on the far right, I would think about the octet rule.

[ElectroMaster88]

Yes, we talked about the octet rule in the class, but by that rule, the second from the left compound should be impossible too, no?

[Babcock_Hall]

I don't see a violation in the octet rule in the structure of the compound that is second from left.  It would be high in energy, and it would presumably have a positive charge.