Question

take 50ml of water with the measuring jar and pour it in a glass.mark the level of water on the glass and throw it out
now measure 50ml of milk with measuring jar and pour it in the same glass mark the level of the milk on it
1---are the levels of milk and water same?
remove the milk from the glass.now pour oil into the glass upto the level marked for water\
2--can u guess the volume of oil

Answer 1

no weight of water and milk is not same. weight of milk is higher then water. because the milk has high density then water.
and for oil less volume bcoz density of oil is less than the water.
mass of the sub. is depends on vol. & density  
d=m       d = density
    v        m= mass
              v = volume
    

Answer 2

    We are measuring 50 ml of water or 50 ml of milk or 50 ml of oil with the same measuring jar.  So the quantity in volume is same.  Ideally when these liquids are poured into the same glass separately, all the liquids will rise up to the same glass mark/level.  Ideally the volume of oil in the glass is also 50 ml.

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in reality:
    Due to higher viscosity, oil does not completely get poured into the glass. some oil remains in the measuring jar as it sticks to the walls and the bottom of the jar.   But  Water has the least viscosity of the three liquids, so most of it gets into the glass.