Step 1: Understand London forces.
London forces are weak pulls between non-polar molecules. They get stronger when a molecule is bigger and when it has more surface to touch its neighbours.
Step 2: Compare the sizes first.
Isobutane is $\text{C}_4\text{H}_{10}$, with only 4 carbons. The other three are pentanes, $\text{C}_5\text{H}_{12}$, with 5 carbons. More carbons means more electrons and stronger London forces, so isobutane is the weakest and is ruled out.
Step 3: Now compare the three pentane shapes.
n-pentane, isopentane and neo-pentane all have the same formula but different shapes. Shape decides surface area.
Step 4: Think about straight versus branched.
A straight chain is long and open, so molecules can lie close along each other and touch over a big area. A branched molecule is more like a ball, so it touches less.
Step 5: Rank them.
n-pentane is fully straight, so it has the largest touching area. Isopentane has one branch and neo-pentane is the most branched and ball-like, so it touches the least.
Step 6: Pick the strongest.
The biggest touching area gives the strongest London forces. So n-pentane has the strongest London forces among these.
\[ \boxed{\text{n-pentane}} \]