In which of the following situations would a writer most likely use informal language?

a. writing a letter to a friend who is stationed in the military overseas.
b. writing a letter of interest for a job application.

c. writing an essay for a college entrance application.
d. writing a letter to a supervisor requesting a letter of recommendation

A. Writing a letter to a friend who is stationed in the military overseas.

Explanation:

Informal language is used when we talk or converse with our friends, family and the people we are comfortable and familiar with. It needs no form of formality in it. Whereas formal language is mainly used in the business and professional spheres. It does not use the casual language that is used in informal settings.

So, out of the options provided in the question, option A is the right answer for a letter to a friend can be written in an informal language and tone. Likewise, options B, C and D are all part of the formal language, for they are about job application, college essays and official letters.