The number of $$\sigma$$ bonds, $$\pi$$ bonds and lone pair of electrons in pyridine, respectively are:

In Lassaigne's extract of an organic compound, both nitrogen and sulphur are present, which gives blood red colour with $$\mathrm{Fe}^{3+}$$ due to the formation of-

Amongst the given options which of the following molecules/ion acts as a Lewis acid?

Consider the following compounds/species:

The number of compounds/species which obey Huckel's rule is ___________.