Which of the following compounds of lead is used in the match industry?

With respect to graphite and diamond,which of the statement$(s)$ given below is (are) correct?
$(A)$ Graphite is harder than diamond.
$(B)$ Graphite has higher electrical conductivity than diamond.
$(C)$ Graphite has higher thermal conductivity than diamond.
$(D)$ Graphite has higher $C-C$ bond order than diamond.

Silicon has a strong tendency to form polymers like silicones. The chain length of silicone polymer can be controlled by adding :-

What is the value of $\angle S-S-S$ in the puckered $S_8$ ring of rhombic sulfur (in $^{\circ}$)?

$A$ crystalline solid $X$ reacts with dil. $HCl$ to liberate a gas $Y$. $Y$ decolourises acidified $KMnO_4$. When a gas $Z$ is slowly passed into an aqueous solution of $Y$,colloidal sulphur is obtained. $X$ and $Z$ could be,respectively

$(1)$ Half-life of $^{14}C$ is $...........$
$(2)$ $..........$ isotope of carbon is used in radiocarbon dating.
$(3)$ Main component of ceramic,cement and glass is $........$