What would happen if graphene is heated in sufficient supply of air?

Have you ever observed while cleaning cloth that foam is formed with difficulty and an insoluble substance (scum) remains after washing with water? This is caused by the reaction of soap with the calcium and magnesium salts, which cause the hardness of water. Hence, you need to use a larger amount of soap. This problem is overcome by using another class of compounds called detergents as cleansing agents. Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water. Thus, they remain effective in hard water. Detergents are usually used to make shampoos and products for cleaning clothes.

(i) How will you test the hardness of water?

(ii) Why soap forms scum (insoluble substance) with hard water?

(iii) How one can overcome the problem of scum formation? What values do you identify in this context?

Consider the following statements related to diamond and graphite.

I. Both diamond and graphite are used as abrasives.

II. Diamond and graphite have different arrangements of carbon atoms.

III. The carbon atoms in graphite have a different number of neutrons from those in diamond.

IV. The carbon atoms in both graphite and diamond have four single covalent bonds. The incorrect statement(s) is/are

C⁴⁺ does not exist but Pb⁴⁺ exists although both belong to the same group. This is because

I. size of carbon is much smaller than Pb. II. large amount of energy is needed in case of carbon.

III. of inert pair effect.

IV. nucleus cannot hold such a large number of electrons.

The correct statement(s) is/are

The structures of three hydrocarbons are given below

Which statement is correct for all the above three compounds?