This is not easy. For many of the chemical elements there are several known isotopes. Isotopes are atoms with different atomic masses which have the same atomic number. The atoms of different isotopes are atoms of the same chemical element; they differ in the number of neutrons in the nucleus.
To test for hydrogen, burn a candle near the suspected source of hydrogen. If you hear a squeaky pop sound, hydrogen is present because when hydrogen gas burns, it makes a squeaky pop sound.
<u>Answer:</u> In heterogeneous mixture, the composition remains variable throughout.
<u>Explanation:</u>
For the given options:
Homogeneous mixtures are defined as the mixtures that appears uniformly throughout the solution and the particle size or shapes are not different. The composition remains constant throughout.
A solution is defined as the solution in which the components gets completely dissolved in it. Particles are evenly spread in these solutions. These solution does not scatter light falling on it. The composition remains constant throughout.
An amorphous solid is defined as the solid in which the constituent particles of the matter are arranged in the random manner. The composition remains constant throughout.
A heterogeneous mixture is defined as the mixture in which component are unevenly spread throughout the solution. The size and shape of the particles differ in these mixtures. These mixture scatter the light falling on it. The composition do not remains constant throughout.
Compound is defined as the chemical specie which is formed by the combination of two or more different type of atoms. <u>For Example:</u> 
etc...The composition remains constant throughout.
Hence, in heterogeneous mixture, the composition remains variable throughout.
It is true that when a distance between gas particles increases, the volume of the gas will also increase.
Answer: Option A
<u>Explanation:</u>
The volume of any material can be the space occupied by any material. And the space required by any material to occupy a desired shape or size is determined by its bonding and distance between the particles making that material. If the particles which are soft and small can be compressed easily to occupy very small volume compared to compound made up of hard and large particles.
Along with this, the distance between the neighbouring particles also play a major role, as if we consider a laddo, we can compress it to small size by reducing the distance between neighbouring particles while we will not be able to compress the size or volume occupied by a table as we cannot reduce the distance of particle separation. Thus, it is true that if the distance between gas particles increased then the volume of gas particles will also increase.
