Which of the following alkoxide and alkyl halide pairs give the stated ether in good yield by the Williamson synthesis?

The halide must be methyl or primary (or at least unhindered) for SN2. Pair 1 uses methyl iodide and pair 2 uses a primary bromide with a phenoxide, so both succeed. A tertiary halide with methoxide undergoes E2 to isobutene, and an aryl halide does not undergo SN2 because backside attack at an sp2 carbon is impossible.