The best Spanish translation of the singular masculine form of the following possessive pronoun 'His' is Option 4: Su.
What is the translation?
Su is the possessive adjective corresponding to the third person singular masculine pronoun "él" (he). It implies that someone else owns something. Nuestro means "our" and refers to a group of people including the speaker.
Tu means "your" and is used to address one person directly in a singular and informal way. While su can also be interpreted as "her" or "its" depending on the context, it is the most accurate translation for "his" in the singular masculine sense.