In the first line, hayden mentions selma. this is a reference to the 1965 civil rights march from selma, alabama, in which nonviolent protestors were attacked by police.

today as the news from selma and saigon
poisons the air like fallout,
i come again to see
the serene great picture that i love.

–“monet’s ‘waterlilies,’”
robert hayden

what type of figurative language is the use of the word selma here?
allusion
metaphor
simile

how does this example of figurative language affect the last line of the stanza?
it creates suspense
it sets up a contrast
it provides a description

First part is allusion.

Second part is It sets up contrast.

The type of figurative language  represented by the use of the word Selma in the provided stanza is allusion.

Allusion is a brief and indirect reference to a person, place, thing or idea of historical, cultural, literary or political significance, in this particular case  the 1965 civil rights march from Selma, Alabama, in which nonviolent protestors were attacked by police.  Allusions are just passing comments about which the writer expects the reader to possess enough knowledge to noticeits importance in a text.

The use of such figurative language affects the last line of this particular stanza by providung a description. Even though the descriptions referred to persons or things in allusions are not fully detailed, its use enables writers or poets to simplify complex ideas and emotions.

lemme actually be useful and say i believe the answer is the first one.