What type of mixtures are separated by the technique of crystallisation?

Classify the following as chemical or physical changes:
$1$. Cutting of trees
$2$. Melting of butter in a pan
$3$. Rusting of almirah
$4$. Boiling of water to form steam
$5$. Passing of electric current through water and the water breaking down into hydrogen and oxygen gases
$6$. Dissolving common salt in water
$7$. Making a fruit salad with raw fruits
$8$. Burning of paper and wood

Which of the following will show 'Tyndall effect'?

Which of the following materials fall in the category of a 'pure substance'?
$(a)$ Ice $(b)$ Milk $(c)$ Iron $(d)$ Hydrochloric acid $(e)$ Calcium oxide
$(f)$ Mercury $(g)$ Brick $(h)$ Wood $(i)$ Air.

Differentiate between homogeneous and heterogeneous mixtures with examples.

Pragya tested the solubility of four different substances at different temperatures and collected the data as given below (results are given in the following table,as grams of substance dissolved in $100 \,g$ of water to form a saturated solution).

Substance Dissolved	$283 \,K$	$293 \,K$	$313 \,K$	$333 \,K$	$353 \,K$
Potassium nitrate	$21$	$32$	$62$	$106$	$167$
Sodium chloride	$36$	$36$	$36$	$37$	$37$
Potassium chloride	$35$	$35$	$40$	$46$	$54$
Ammonium chloride	$24$	$37$	$41$	$55$	$66$

$(a)$ What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in $50 \,g$ of water at $313 \,K$?
$(b)$ Pragya makes a saturated solution of potassium chloride in water at $353 \,K$ and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.