You can find help from: https://www.enotes.com/topics/ralph-ellison/critical-essays/analysis-1 for analysing.
'Iamb' refers to the sequence of unstressed and stressed syllables, and 'pentameter' means that there are ten syllables (penta means five, so you just multiply it by two). So the correct answer is 'ten syllables divided into pairs of unstressed and stressed syllables'.