Learn Icelandic: Þetta er ekki hópur svína. - This is not a group of pigs.

svína is the genitive plural form of the neuter noun svín (pig). In Icelandic, the genitive case is used to show possession or composition, which translates to the "of" in "a group of pigs".

Is -a the standard ending for the genitive plural?

Yes! For almost all bare nouns (nouns without "the" attached), regardless of whether they are masculine, feminine, or neuter, the genitive plural ends in -a. So the base word svín simply becomes svína.

Why do we use the neuter pronoun Þetta (this) when hópur (group) is a masculine noun?

When you introduce what something is using "This is..." or "That is...", Icelandic always uses the default neuter singular pronoun Þetta. It doesn't change to match the gender of the noun being introduced.

What case is hópur in here?

It is in the nominative case. The verb er (is) acts like an equals sign, so the noun on both sides stays in the nominative case. The adverb ekki (not) doesn't change this rule.