Draw the alkyne you would start with to synthesize pentane. draw the molecule on the canvas by choosing buttons from the tools (for bonds and charges), atoms, and templates toolbars.

Structure of alkynes has been shown below

Explanation:

Alkynes are fully hydrogenated to alkanes by and a metal catalyst e.g. Raney Ni, Pd-C etc.

Here alkynes get stuck onto metal catalyst surface leading to complete hydrogenation of triple bond by .

Reaction occurs in SYN-addition fashion where adds onto unsaturated bond from same side.

Full reaction scheme has been shown below.  

a polar bond is formed when electrons are shared unevenly between atoms