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

Which gas is useful for inhibiting bacterial growth?

Which of the following properties of $H_2$ (dihydrogen) gas is $NOT$ correct?

$(a)$ Give an example of a combination reaction which is exothermic.
$(b)$ Identify the oxidizing agent and reducing agent in the following reaction:
$H_{2}S + Cl_{2} \rightarrow 2HCl + S$
$(c)$ Name the phenomenon due to which the taste and smell of oily food changes when kept for a long time in the open. Suggest one method to prevent it.

$2Na_{(s)} + 2H_2O_{(l)} \longrightarrow ?$

What is the chemical formula for potassium dichromate?