In the line, “a heart whose love is innocent! ” the word “heart” is used as
a)sibilance
b)metonymy
c)personification
d)synecdoche

The answer is: d) synecdoche  

Synechdoche is a figure of speech in which part of something is used to represent the whole, or vice versa.

In the line from the poem "She walks in Beauty," the author Lord Byron attributes the heart as a depiction of an entire person. Therefore, the woman's heart has feelings of innocent love.

chapter i -- paris: september, 1792

a surging, seething, murmuring crowd of beings that are human only in name, for to the eye and ear they seem naught but savage creatures, animated by vile passions and by the lust of vengeance and of hate.

during the greater part of the day the guillotine had been kept busy at its ghastly work: all that france had boasted of in the past centuries, of ancient names, and blue blood, had paid toll to her desire for liberty and for fraternity.

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