Reaction between a carbene and n-pentane
n-Hexane is one of the 3 products formed. Carbenes are high-energy, reactive intermediates.  Due to their extreme reactivity they usually react indiscriminately. In the case of methylene (the carbene in your diagram), it will insert into each of the different $\ce{C-H}$ bonds that are present in n-pentane.  Because of its reactivity, the 3 products will be formed in a statistical ratio that is roughly equivalent to the number of different hydrogens present in the starting n-pentane, 6:4:2.

If you'd like to learn more about carbenes, for example

singlet and triplet carbenes
their addition to carbon-carbon double bonds

then take a look at these earlier answers - ref_1, ref_2