Define physical change and chemical change. state which type of change occur in each of the following statemenet:
(a) passing an electric current through molten magnesium chloride yields moltenm magnesium and gaseous chlorine.
(b) the iron in discarded automobiles slowly forms reddish brown, crumbly rust.

Physical change: It is reversible process and we can get back to orginal material. Best example is the interconversion of ice into water which inturn into vapour.

Chemical changes are irreversible and we can't get back the original material. Example combustion of coal, rusting of iron

Explanation:

1. Electrolysis of molten MgCl2 is chemical change since we can't get back MgCl2 after Electrolysis and new materials are formed.

2. It is an example rusting of iron comes under chemical changes.

in scientific notation, the value of the  speed of light in a vacuum

  will be written as 2.995 * 10^8. when this value is represented in the form of

  a * 10^b, then, a = 2.995 and b = 8.

the value of the speed of light in a vacuum given above can also be rounded up to approximately 300000000. in this case, the scientific notation will be written as 3 *10^8.

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.