It is a very old word, Old or Middle English, and is irregular, like "child and children", and hasn't changed over the centuries. This ending -en on a noun is very rare. You can't say "oxes".

Old English oxan, plural of oxa, was very common, appearing in the psalter, the bible, and laws, among other places, although the spelling oxen is attested in only one place, in a document relating to Bury St Edmund's possessions, rents, and grants.

The genitive plural form of oxa, often with a syncopated vowel, was ox(e)na. That genitive form is attested in place names (cf. oxenaford, Middle English Oxenford, ModE Oxford, oxeneham ModE Oxnam, oxenesetene ModE Oxsettle Bottom, oxnaleage ModE Oxleigh and Oxley , a woodland clearing or a natural glade, meadow, lea, a plant name oxna-lib glossing Latin oleotropius ModE oxlip, ox-heal), as a unit of measure of land (oxnagang, ModE ox-gang, one-eighth of a "hide"), and in genitive (oxna-paeþ ModE oxens' path) and partitive genitive constructions (ic bohte fif getymu oxena, ic bohte an getyme oxena, ModE I bought five teams of oxen, I bought one team of oxen) and those uses appear not only in texts dealing with quotidien farming and mercantile situations but notably in passages from the Bible, which would frequently have been heard by audiences from all social and economic classes.

The plural appears as oxen and is very well-attested in Middle English in a wide range of texts. It appears in various spellings, including oksen, exen, oxon, oxen, oxsen, oxsin, ocsen (see the MED). Its appearance in proverbial contexts (Moche uolk of religion zetteþ þe zuolȝ be-uore the oksen. Many people of religion set the plow before the oxen) and laws is very strong evidence that it was widely used.

P.S. I have a copy of the Old English corpus and found these attestations by searching it. (I studied Old English and Middle English as an undergraduate and graduate student, back before the days of personal computers, but they haven't changed much in the interim.)

P.P.S. I stumbled upon a book, Working Oxen by Martin Watts. 1999. "... a survey of their use in Britain, their impact upon the countryside, and the relics that can still be found: yokes, bows, shoes, housing and place-names. Martin Watts is curator of the Ryedale Folk Museum in North Yorkshire." [Google Books description] and "Oxen were one of the most important sources of motive power in the British countryside... The working ox has left a lasting mark on the language, landscape and culture... Historians rarely mention or study them. It is as if a history of twentieth century were to ignore the impact of the tractor and the lorry. The purpose of this book is to redress that balance." [from the blurb on Amazon].

Final Answer: The plural of "ox" is "oxen," which is an example of an irregular plural form in English. Unlike regular plurals that typically add an "s," the plural of ox changes altogether. The correct answer to the question is C. oxen . ; Explanation: The plural of "ox" is "oxen." In English, many nouns can form their plural form by simply adding an "s" at the end, but there are irregular nouns that do not follow this standard rule. The word "ox" is one such irregular noun. Here's how we can understand this: Singular and Plural Forms : The singular form "ox" represents one animal, while the plural form "oxen" represents two or more of these animals. Irregular Patterns : Unlike regular plurals which follow simple rules, irregular nouns may change forms completely or follow unique patterns. For example, the plural of "mouse" is "mice," and similarly, the plural of "ox" is formed by changing the ending to "-en." Historical Context : The word "oxen" is rooted in Old English, where the plural form used to end in "-n." This pattern has persisted in modern English as well. This makes the correct answer to the multiple-choice question C. oxen . If you encounter other strange plural forms, it could be helpful to look them up in a dictionary, especially since English has many exceptions to the rules! ; Examples & Evidence: Examples of other irregular nouns include 'child,' which becomes 'children,' and 'foot,' which becomes 'feet.' This shows how some nouns change form instead of just adding 's'. The formation of the plural 'oxen' is documented in standard English dictionaries, confirming its use as an accepted plural form.

"The correct answer is option 2) i.e. Oxen. Explanation 'Ox' is a domestic bovine (having qualities characteristic of cows) mammal. The plural form of 'Ox' is 'Oxen' because some nouns adopt foreign rulings. The Foreign Plural nouns have irregular plural forms. They often make their plurals according to the rules of the language they were taken from (e.g. Latin or Greek or German). Sometimes there is more than one plural form possible or these forms have different meanings. For example:   Singular Plural analysis analyses appendix appendixesappendices axis axes basis bases ox oxen child children datum data phenomenon phenomena   Hence, the correct plural form of the given word is 'Oxen'. A few words take -en instead of -s or -es to become plural: We may have heard that English is a Germanic language. The -en ending on plurals is something we get from the German roots. In Old English, some nouns were made plural with -s and -es as they are today, but many nouns took -en to become plural. By the 14th century, the s-form became dominant everywhere, but people didn't let go of the en-form completely; as late as the 16th century the plural of the eye was eyen and the plural of hose was hosen. Today only a few en-forms survive; the most common are oxen and children."