Which among the following poems has not been composed by P.B. Shelley?

The correct option is When We Two Parted.

To understand why this is the correct answer, let's analyze the authorship of each of the poems listed in the options:
1. To Wordsworth: This is a sonnet written by the English Romantic poet Percy Bysshe (P.B.) Shelley, first published in his 1816 collection Alastor, and Other Poems. In it, Shelley expresses his grief and disappointment over William Wordsworth's transition from a revolutionary poet to a conservative supporter of the establishment.
2. Mutability: This is another famous poem composed by P.B. Shelley, also published in his 1816 collection. It explores the Romantic theme of impermanence and how change is the only constant in human life.
3. Hymn to Intellectual Beauty: Written by P.B. Shelley in the summer of 1816 and published in 1817, this poem explores his philosophical concepts of a spiritual force or beauty that exists beyond the material world.
4. When We Two Parted: This lyric poem was actually written by George Gordon Byron, commonly known as Lord Byron, another major figure of the Romantic movement. It was written in 1808 and published in 1816, expressing the poet's grief and regret following the end of a secret love affair.

Therefore, because "When We Two Parted" was composed by Lord Byron and not P.B. Shelley, it is the correct answer.