Which of the following,on reaction with water,will have a $pH$ less than $7$?

Which of the following is true for diamond?

Explain the reactivity of group $14$ elements towards oxygen.

Concentrated hydrochloric acid,when exposed to air,sometimes produces a white cloud of smoke. What is the explanation for this?

What are the $C-C$ single bond length and double bond length in fullerene?

Match the following:
| List-$I$ | List-$II$ |
| :--- | :--- |
| $A$. Carbon black | $I$. Electrodes in batteries |
| $B$. Graphite | $II$. Extraction of metals |
| $C$. Diamond | $III$. Abrasive |
| $D$. Activated charcoal | $IV$. Filler in automobile tyres |
| | $V$. Air conditioning system |