$(a)$ Define an element.
$(b)$ Identify non-metals from the following elements: Carbon,Potassium,Silicon,Chlorine,Mercury.

How is heating of sugar and heating of ammonium chloride different from each other? Explain your answer.

Classify the following into elements,compounds,and mixtures:
$(a)$ Sodium $(b)$ Soil $(c)$ Sugar solution $(d)$ Silver $(e)$ Calcium carbonate $(f)$ Tin
$(g)$ Silicon $(h)$ Coal $(i)$ Air $(j)$ Soap $(k)$ Methane $(l)$ Carbon dioxide $(m)$ Blood

What are the favourable qualities given to gold when it is alloyed with copper or silver for the purpose of making ornaments?

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

Rusting of an article made of iron is called: