Is l'idee masculin or feminine in French?

" l' " can be masculine or feminine. It stands for "le" (masc.) or "la" (fem.) when the following noun begins with a vowel sound.

une option (fem.) : l'option.
un abribus (masc., meaning a bus shelter) : l'abribus
l'élève (the pupil): it could be "un élève" or "une élève" (you have no gender indication here)