Answer: The chemical name of Sindoor is Vermillion having the chemical formula as Pb3O4.
Sindoor or Vermillion is red in colour as it is made up by crushing lead and mixing or reacting it with oxygen. The lead in it gives it its bright red colour. Different shades can be made of sindoor by just having different reaction timing and different quantities of lead and oxygen.
Moreover, sometimes Cinnabar is used which comes from the ore of mercury which is quite poisonous. Therefore, before using it, it is first distilled and refined. Cinnabar also contributes towards the red colour of sindoor.