1. El lápiz
El lápiz translates into the pencil. So, this is a singular form. The definite article el matches masculine and singular nouns. In this way, lápiz is a masculine and singular noun. Recall that the definite article is used when thinking that the reader or listener knows which particular thing or person we are talking about, perhaps because we have already mentioned it. The plural and masculine form of the definite article is los and the plural form of lápiz is lápices. Therefore:
Los lápices
2. La nariz
La nariz translates into the nose. So, this is a singular form. The definite article la matches feminine and singular nouns. In this way, nariz is a feminine and singular noun. The plural and feminine form of the definite article is las and the plural form of nariz is narices. Therefore:
Las narices
3. El profesor
El profesor translates into the teacher. So, this is a singular form. The noun profesor is masculine, so we need to use the masculine definite article as well, which is el. To write this using the definite article and noun in their plural forms, we need to change el into los and profesor into profesores
Los profesores
4. El ratón
El ratón translates into the mouse. So, this is a singular form. The noun ratón is masculine, so we need to use the masculine definite article as well, which is el. To write this using the definite article and noun in their plural forms, we need to change el into los and ratón into ratones
Los ratones