Why do fireflies glow at night?

Evaporation of petrol is a physical or chemical change?

Burning of Liquefied Petroleum Gas (LPG) is a physical or chemical change?

 Heating of an iron rod to red hot is a physical or chemical change?

Curdling of milk is a physical or chemical change?

Sublimation of solid ammonium chloride is a physical or chemical change?

During the reaction of some metals with dilute hydrochloric acid, following observation were made. Explain this observation giving suitable reasons.

 Silver metal does not show any change.

During the reaction of some metals with dilute hydrochloric acid, following observation were made. Explain this observation giving suitable reasons.

The temperature of the reaction mixture rises when aluminium $\left(\mathrm{Al}\right)$ is added.