Which of the following can chlorine not displace?

Which halogen is known to cause the reaction given below:
$2 Cu^{2+} + 4 X^{-} \rightarrow Cu_2 X_{2(s)} + X_2$

Which element from the following combines with hydrogen to form a compound with the lowest thermal stability?

Artificial smoke screens are made by

One of the hydrolysed products of the following compound does not react with the silica of a glass vessel.

Find out which of the following statements are true or false:
$(a)$ Number of $S-S$ bonds in $H_2S_nO_6$ is $(n-1)$.
$(b)$ When $F_2$ reacts with $H_2O$,it forms $HF$,$O_2$,and $O_3$.
$(c)$ $XeF_6$ on hydrolysis shows a disproportionation reaction.
$(d)$ $Al$ metal on reacting with dilute $NaOH$ gives a white precipitate of $Al(OH)_3$ as a final product.