(a) Strontium salts burn produces a reddish colour flame. (b) Barium sulphate is used in medical procedures because it does not dissolve in water or other body fluids, so it is used to examine the alimentary canal of a patient by X-ray. (c) Magnesium is the powerhouse behind photosynthesis in plants. Without magnesium, chlorophyll cannot capture sun energy needed for photosynthesis. (d) Red colour of gemstone Ruby is due to the element chromium present in it. The more chromium, the stronger the red colour. Hence, option (d) is not true.