The square brackets are used in case of complex compounds. This is known as coordination sphere. There is a metal in the coordination sphere and ligands attached to it. This complete set of metals and ligands inside the brackets is complex ion or molecule.
The ions outside this coordination sphere are counter ions of the complex.
It represents that if the complex compound is dissolved in water it will give a complex ion and the counter ion. The atoms in the bracket cannot break there bonds and will remain un-dissociated.
If there is no such bracket then it will represent simple or binary salt.
Answer:
There is a physical change as the water is evaporating, producing a gas.
<span>The balloons volume as it
rises increases because at higher altitude external pressure is lower, so the
air molecules inside the balloons tends to expand more to attain mechanical
equilibrium, where the external pressure and internal pressure are equal. Unlike
when the balloon is on the ground, external pressure is great so the gas
molecule cannot push the walls of the balloon so it is like underinflated.</span>
