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The new volume of the hydrogen gas in the balloon is 1.5 L.
<u>Explanation:</u>
At STP, Temperature, T1 is 0° C = 0 + 273 K = 273 K
Pressure, P1 = 1 atm
Here given volume, V1 = 3.60 L
Balloon at sea,
Pressure, P2 = 2.5 atm
Temperature, T2 = 10° C = 10 + 273 = 283 K
Volume, V2 = ?
Here, we have to use the equation,

We have to rearrange the equation to get V2 as,

Now plugin the values as,
V2 = 
= 1.5 L
So the new volume of the hydrogen gas is 1.5 L.

Volume of 20 g of hydrogen at normal temperature and pressure (NTP) = 240.55 ml.

The atomic number is 11. The atomic number will always be the same as the number of protons and electrons.
Caesium sulfate (cesium sulfate) is the inorganic compound and salt with the formula Cs2SO4. It is a white water-soluble solid that is used to prepare dense aqueous solutions for use in isopycnic (or "density-gradient") centrifugation. It is isostructural with potassium salt.