“Carbonium ion is any cation that has a pentavalent carbon atom” e.g., CH5+
In older literature the name “carbonium ion” was used for what is today called carbenium ion. The current definitions were proposed by the chemist George Andrew Olah in 1972 and are now widely accepted.
Carbonium ions can be obtained by treating alkanes with very strong acids.
So, what is hybridisation of CH5+ ??