Question

suggest a seperation technique for d foll mixtures
-mercury and water
-potassium chloride and sodium chloride
-common salt ,water and sand
-kerosene oil ,water and salt

Answer 1

-mercury and water
let mixture sit, Hg will drop to bottom (denser), suction water out with pipette/syringe

-potassium chloride and sodium chloride
hm the only way i can think of this is by collecting the metal (K or Na) with the lower reduction potential on an electrode by applying enough voltage (but not so much that the other also deposits on the electrode). The problem with is that you will need a Pt of Au electrode to redissolve the metal collected and not the electrode itself (you could use HNO3 to redissolve it).

-common salt ,water and sand
filter to get sand out, distill to get water out

-kerosene oil ,water and salt
let mixture sit, kerosene and water will separate due to one being hydrophobic and one hydrophilic (the denser one will be at the bottom), wait for it to settle and suction out whichever is on top (like in #1). Common salt will only be dissolved in the hydrophilic phase (water), so distill hydrophilic phase after that.