Question 3 :
Why crystallisation is used as a method of obtaining pure $CuSO_4$ from impure sample?

Question 8 :
Consider the list of follwing substances. How many of the following are pure substances?<br>oxygen, fluorine, paints, hydrochloric acid, methane

Question 11 :
The most suitable method of separation of $1$ mixture of ortho and para-nitrophenols is:

Question 12 :
.................. is the change of gaseous state directly to solid state without going through liquid&#160;the state.<br/>

Question 13 :
Dicky, Micky and Vicky had three liquids, $A, B$ and $C$ respectively. They mixed these liquids and observed that they form a homogeneous mixture. They were unable to separate the liquids and asked their teacher to separate these for them. The teacher subjected the given mixture to fractional distillation. Liquid $B$ was obtained in the receiver flask. On further distillation, $A$ was left behind in the distillation flask. On the basis of the result, arrange the critical temperatures of $A, B$ and $C$ in their respective gaseous states in proper order.

Question 16 :
Which one of the following mixtures can be separated into pure components by fractional distillation?

Question 19 :
Centrifugation is a process which involves the use of the centrifugal force for the sedimentation of heterogeneous mixtures with a centrifuge used in industry.

Question 20 :
Out of the following fractions of petroleum, the one having the lowest boiling point is or Which of the following is obtained at lowest temperature by fractional distillation of petroleum<br>