Learn Spanish (Latin America): Ese porcentaje de la población es diferente. - That percentage of the population is different.

Eso is a neuter pronoun used for abstract ideas, statements, or unknown objects. Because we are pointing directly to a specific masculine noun in this sentence (porcentaje), we must use the masculine singular adjective ese.

How can I remember that porcentaje is a masculine noun?

While Spanish nouns ending in -e can be unpredictable, words ending in the suffix -aje (like porcentaje, viaje, and mensaje) are almost always masculine. That is why it pairs with Ese.

Is there a reliable rule for the gender of población?

Yes! Nouns that end in -ción (as well as -sión) are consistently feminine. That is why it requires the feminine article la.

Why do we use es instead of está with diferente?

We use es (from the verb ser) because we are describing an inherent characteristic or mathematical fact about this percentage, rather than a temporary state or condition.