The word bubble is scanned as
an iamb
a dactyl
an anapest
a trochee

A trochee.

Explanation:

Meter in poetry or in verse is basically the rhythmic pattern of stressed an unstressed syllables.

There are five types of Meter in English poetry:

Anapestic Meter- It is a three syllable metrical pattern. It contains of two unstressed followed by one stressed syllable. Dactylic Meter- It is also three syllable metrical pattern contained with one stressed syllable followed by two unstressed syllable. Iambic Meter- It is a two syllable metrical pattern of unstressed syllable followed by stressed syllable. Spondaic Meter- This metrical pattern contains of two stressed syllable, making it to be a 'two syllable metrical pattern'. Trochaic Meter- This metrical pattern is also two-syllabic metrical pattern of stressed syllable followed by unstressed one.

The word Bubble is an example of trochee, as it contains two syllables.

'Bub' is the stressed syllable followed by 'ble' which is unstressed.

So, the correct answer is last option 'a trochee'.