Questions

A simile is a figure of speech in which two different things are compared using like or as words.

Here in the given sentence, Foam brightens like the dogwood foam's brightness is compared to dogwood. Hence, it is a simile.

Electronegativity is the tendency for an atom to attract electrons. There are general trends on the periodic table which you can use to determine the relative electronegativity for different elements, but otherwise you can also look at their valence shell and effective nuclear charge to determine their relative electronegativity.

Here from the given options, Lithium has least tendency to attract electrons and thus has a lower electronegativity.