Which of the following represents the correct combination of the prefix 'anti' with the root word 'matter'?

The correct combination of the prefix 'anti' with the root word 'matter' is represented as "antimatter." This term is correctly formed by attaching the prefix directly to the root word without any additional letters or modifications, which conform to standard conventions of English word formation.

The prefix 'anti-' means 'against' or 'opposite,' and when combined with 'matter,' it describes a type of matter that is the opposite of ordinary matter, as used in physics. This makes "antimatter" an established term in both scientific and general usage.

Other forms, such as "anti-matter" with a hyphen, may be seen in informal contexts but do not reflect the standard usage in scientific literature. The spellings "antymatter" and "antimattr" do not conform to recognized English spelling rules or the established terminology related to physics, thus making "antimatter" the only correct form.