Which of the following are chemical changes?
$(i)$ Decaying of wood
$(ii)$ Burning of wood
$(iii)$ Sawing of wood
$(iv)$ Hammering of a nail into a piece of wood

$(a)$ State the difference between a pure substance and a mixture. Give one example of each.
$(b)$ Identify homogeneous mixtures from the following:
$(i)$ Smoke
$(ii)$ Brass
$(iii)$ Tincture of iodine
$(iv)$ Milk

Based on which factor is a solution said to be dilute,concentrated,or saturated?

The teacher instructed three students '$A$','$B$',and '$C$' respectively to prepare a $50\%$ (mass by volume) solution of sodium hydroxide $(NaOH)$. '$A$' dissolved $50\, g$ of $NaOH$ in $100\, mL$ of water,'$B$' dissolved $50\, g$ of $NaOH$ in $100\, g$ of water,while '$C$' dissolved $50\, g$ of $NaOH$ in water to make $100\, mL$ of solution. Which one of them has made the desired solution and why?

The substances that sublime easily are

How are colloids different from suspensions? Identify the colloids from the following: Soda water,milk,sponge,clouds,mixture of alcohol and water,jelly.