Simplify the following text for a Grade 7 native English-speaking person.
Original: A molecular cloud , sometimes called a stellar nursery if star formation is occurring within , is a type of interstellar cloud whose density and size permits the formation of molecules , most commonly molecular hydrogen ( H2 ) .
Simplified: A molecular cloud is a kind of cloud in space . It has enough density and size so that molecules can form , usually molecules of hydrogen ( H2 ) .