A sentence of mine was corrected, and I'm not sure what was wrong with it. I said "Yo tengo mucho hambre." and someone said I should have used mucha instead. I'm not sure what the difference is 🤔

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The correct sentence is "Tengo mucha hambre". In Spanish we usually drop pronouns and nouns have genders. "Tengo mucha hambre" literally means "I have hunger". The word "hambre" is a feminine noun despite the fact that you must use a masculine article and say "el hambre" (the hunger). This is so because saying "la hambre", with a feminine article, would sound awkward to native speakers. This phenomenon is known as "a tónica", "hambre" is a feminine noun that's stressed in the first syllable "hAm", so you have to use the masculine article "el", however, it's still a feminine noun, and that's why the adjective "mucha" has to agree with the gender of "hambre". The same thing happens with other words like "el agua", it's a feminine noun even though you have to use a masculine article because of the "a tónica" and say, for example, "El agua está limpia" (The water is clean). I hope this makes sense