Answer:
solid is the substance which is hard
liquid is the substance which we get in liquid form for example water milk etc
gases are those substance which we cannot touch and see
Popping noise,difrent odor,fizzing and stuff like thwy
3; When counting significant figures, all nonzero numbers are significant, and any zero that is behind a decimal point is also significant.
<u>Answer:</u> The correct option is
<u>Explanation:</u>
A catalyst is defined as the chemical species that increases the reaction rate but does not participate in it and is left behind after the completion.
A homogeneous catalyst is one that is present in the same phase as the reactants and products.
A heterogeneous catalyst is one that is present in different phase as that of reactants and products.
For the given chemical reaction:

As all the reactants and products are in gaseous state so, the homogeneous catalyst must also be in the gaseous state only.
Hence, the correct option is 
I would say 4 but you can figure it out or if you have a parent near by to