Q28 of 44 Page 5

Why do fireflies glow at night?


Fireflies have a luminous bag at their lower abdomen region that contain a protein called Luciferin. This luminous bag also secretes a certain enzyme called, Luciferase. This enzyme on reaction with Luciferin, emits light in the presence of Magnesium and oxygen. Therefore, fireflies glow in the night.


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26

A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction?

 27

Ferrous sulphate decomposes with the evolution of a gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction.

 29

Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?

 30

Which among the following are physical or chemical changes?

(a) Evaporation of petrol


(b) Burning of Liquefied Petroleum Gas (LPG)


(c) Heating of an iron rod to red hot.


(d) Curdling of milk


(e) Sublimation of solid ammonium chloride