The suggestion is to prevent a puddle of the liquid present in the sample from forming or from it leaking on to the surface on which it is placed. For example, if precipitates of a solid are removed from water and then placed on filter paper to dry, the water will soak into the filter paper and then leak on to the counter on which it is placed. If this precipitate were placed in a watch glass or weighing paper, the water would only evaporate and would not contaminate the sample.
The answer is a cation, I may be wrong but cation is plus and anion is subtract
Density is defined as the ratio of mass to the volume.
Density = 
(1)
Mass of water = 10 grams
Mass of acetone = 10 grams
Density of water = 1 
Density of acetone = 0.7857
Put the value of density of water and its mass in equation (1)
1 = 
Volume of water = 10 
Put the value of density of acetone and its mass in equation (1)
0.7857 =
Volume of acetone = 12.72
Thus, volume of acetone is more than volume of water because the density of acetone is lower.
Explanation:
5 I don't know what is the answer if I got it wrong
Volume of osmium = 1.01(0.223)(0.648) = 0.14595 cm3
Density = mass / volume
So density x volume = mass of osmium
22.6 x 0.14595 = 3.29845 g
