For manufacturing of glass, which among the following is used as a source of silica?

Which among the following is the correct arrangement of halogens in the increasing order of their oxidizing nature?

Copper sulphate crystals available in the market are blue coloured crystals. By careful heating, they turn to white colour. Which one of the following is responsible for the blue colour?

Equal volume of all gases, when measured at the same temperature and pressure, contain an equal number of particles. Who proposed the above law?