1. When the volume of a gas sample is measured it's pressure and temperature must also be specified. why?


2.The practice is normally not necsessary for liqids or solids. why?

3. useing kinetic molecular theory and gas lawsxplain why a weather ballon steadily expand as it rise?

I don't know what level of chemistry you're at, so I'll try to cover this from a couple levels.

The simple answer for 1 & 2 is that the amount of a given volume of a substance varies with temperature and pressure for a gas, but doesn't vary significantly for a liquid (or a solid).

You can fill your tires with a large amount of air without changing the volume if you apply pressure. If you heat the tires (by driving) the pressure will actually change (increase).

Another way of looking at it is via the ideal gas equation. This applies to gases, but not liquids or solids.
PV = nRT
If you want to know the amount of a substance (in moles, n), you need to know all the other parts of the equation. R is a constant, so it is always known. This leaves pressure (P), volume (V), and temperature (T).

As a balloon rises, the pressure decreases. Assuming everything else is constant (it's not, but from the question it sounds like assuming it is what's wanted), we can rearrange the equation:
PV = nRT
V = nRT/P
V = Z/P
where Z is a constant equalling nRT
You can see from this that as P decreases (as the balloon gets higher) V increases because they have an inverse relationship.

Looking at this from a kinetic-molecular standpoint, because the temperature is relatively constant, the average speed of the molecules is unchanged. The pressure is a combination of the speed of the molecules, the number of collisions per unit time with the container walls, and the mass of the molecules (which is also constant). If the speed and mass are constant, the number of collisions must be decreased. Increasing the size of the balloon does this by giving the molecules more distance to travel per collision.