✅ The correct answer is "Surgeon." A common gender noun refers to a person or animal that can be either male or female without the word itself specifying sex. The term "surgeon" applies equally to a male or female practitioner of surgery, and there is no widely accepted or used gender-specific alternative like "surgoness."

❌ "Duchess" is incorrect because it is an explicitly feminine noun (the male counterpart is "Duke").

❌ "Niece" is incorrect because it is an explicitly feminine noun (the male counterpart is "Nephew").

❌ "Sister" is incorrect because it is an explicitly feminine noun (the male counterpart is "Brother").

✅ The noun 'Heir' is a classic example of common gender because it can refer to a person who inherits property or a title, whether that person is male or female, without the noun itself changing form (e.g., 'heir apparent' can be male or female). It specifies a role rather than a biological sex.

❌ 'Duchess' is a specific title for a female noble or the wife of a duke, making it unequivocally a feminine gender noun.

❌ 'Granite' refers to a type of rock, which is a non-living thing; therefore, it is classified as a neuter gender noun.

❌ 'Stallion' specifically denotes an adult male horse, categorizing it as a masculine gender noun.

✅ In English grammar, nouns referring to very young children, such as "infant" or "baby," are traditionally classified as having 'neuter' gender when their specific biological sex is unknown or not being emphasized.

This classification is based on the traditional use of the pronoun "it" to refer to an infant in general contexts where the sex is unspecified, aligning with how inanimate objects or animals of unknown sex are grammatically treated.

❌ "Infant" does not exclusively refer to a male child; it can be either male or female. Therefore, it cannot be classified solely as masculine gender.

❌ Similarly, "infant" does not exclusively refer to a female child. It encompasses both sexes, so classifying it solely as feminine gender would be inaccurate.

❌ While "infant" refers to a human being, 'common gender' nouns (e.g., student, doctor, teacher) typically refer to people whose gender can be male or female, and are often referred to with "he," "she," or "they" (for modern gender-neutrality).

However, for "infant" (and "baby"), the traditional and grammatically recognized pronominal reference when sex is unknown is "it," which is a characteristic of neuter gender in English noun classification, distinguishing it from typical common gender nouns that refer to older persons.

✅ Baby is classified as a common gender noun because it refers to a living being (a human) that can be either male or female. While it is common to use the pronoun "it" for a baby when its sex is unknown or not specified, the noun itself denotes a person, distinguishing it from inanimate objects.

❌ Avalanche is an inanimate natural phenomenon. Nouns referring to non-living things are classified under the neuter gender.

❌ Algorithm is an abstract concept or a set of rules. Abstract nouns and concepts are classified under the neuter gender in English grammar.

❌ Archipelago refers to a group of islands, which are inanimate geographical features. Nouns for inanimate objects fall under the neuter gender.

✅ "Their" is the most appropriate pronoun in modern English for a common gender noun like "applicant" when the individual's gender is unknown or unspecified.

The singular "they" is widely accepted for gender-neutral reference, promoting inclusivity and reflecting current linguistic trends.

❌ "His" functions as a generic masculine pronoun. While historically common, it is now largely considered non-inclusive as it presumes a male identity and excludes other genders.

❌ "Her" would only be appropriate if the applicant were definitively known to be female, or if one were deliberately attempting to reverse the historical generic masculine, but it is not a universally inclusive choice for an unspecified gender.

❌ "His/her" is grammatically correct and inclusive but is often seen as stylistically less elegant or more cumbersome than the singular "their" in contemporary writing, which fulfills the same inclusive function more efficiently.