1) Spectacles: It means a type of eyeglasses which are created to improve people´s eyesight. It is a plural noun as it is modified by “steel” and “rimmed”.
2) Pontoon: it is a temporary, simple boat structure that is used as a bridge. It is a singular noun.
3) Peasants: They are simple and people of low social status who live in the countryside. They usually work on the land, and raise cattle. It is a plural noun.