Which of the following compound is not aromatic?

Aromatic compounds satisfy $(4 n+2) \pi$ Huckel rule. (a) 1,3 -cyclobutene
Number of $\pi$ electrons $=4$ $\because$ It is not equal to $4 n+2$ $\therefore$ It is not an aromatic compound (b) Pyridine
Number of $\pi$ electrons $=6(=4 n+2)$ (Here lone pair of electrons of N does not evolve in delocalisation) (c) Furane
Number of $\pi$ electrons $=4+2=6(=4 n+2)$ (d) Thiophene
Number of $\pi$ electrons $=6(=4 n+2)$ Thus, except 1,3 -cyclobutene, all species are aromatic in nature.