What is the rule for which you can inherit a base class from C# which is being developed in F#?

Answer:

If a language is CLS-Compilant(Common Language specifications), and also if the class developed by using CLS specifications, then it can be inherited in another CLS-Compilant language.Both F# and C# are CLS-Compilant languages. So, it is possible to inherit the base class in C# where the base class is developed in F#.