If bond yields fall by 1% across all maturities, which of the following bonds will increase in value the most?

It's important to understand this as an investor.

There is a metric called "duration". It's the time weighted average of all the coupons and final payment you'd receive over the life of the bond. Logically, a zero coupon bond has the longest duration (equal to its maturity) vs one with coupons, given equal maturities. And the price impact is the change in rate times duration, at the margin. e.g. a 10 year zero will drop about 1% in price for a .1% rise in rate.

So we kill (1) and (2), and go for the 20 year. The higher coupon has a shorter duration, as we get more money back sooner. Therefore it's the 5%, number (4).