$H_2S$ gas changes a filter paper dipped in lead acetate solution into

Which of the following substances is used in smoke screens?

Identify the correct statements among the following:
$a$) $C_{60}$ molecule has $12$ five-membered rings and $20$ six-membered rings.
$b$) $H_2CO_3 / HCO_3^-$ buffer system helps to maintain $pH$ of blood between $7.26$ and $7.42$.
$c$) Graphite is used as a dry lubricant in machines running at high temperatures.

Carbon differs from other elements of the group. Which is the false statement?

Identify the correct statements:
$I)$ $CO$ reduces the oxygen carrying ability of blood.
$II)$ Producer gas contains $CO$ and $N_2$.
$III)$ $C-O$ bond length in $CO_2$ is $115 \ pm$.

Which of the following acids is formed when $SiF_4$ reacts with water?