Deep sea divers use a mixture of ....... for respiration.

Given below are two statements,one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Carbon forms two important oxides $- CO$ and $CO_2$. $CO$ is neutral whereas $CO_2$ is acidic in nature.
Reason $R$: $CO_2$ can combine with water in a limited way to form carbonic acid,while $CO$ is sparingly soluble in water.
In the light of the above statements,choose the most appropriate answer from the options given below:

Which of the following is the correct statement for red lead?

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

Which of the following elements exhibit metallic nature among $C$,$Si$,$Ge$,$Sn$,and $Pb$?

Give reasons:
$(i)$ Conc. $HNO_3$ can be transported in aluminium container.
$(ii)$ $A$ mixture of dilute $NaOH$ and aluminium pieces is used to open drain.
$(iii)$ Graphite is used as lubricant.
$(iv)$ Diamond is used as an abrasive.
$(v)$ Aluminium alloys are used to make aircraft body.
$(vi)$ Aluminium utensils should not be kept in water overnight.
$(vii)$ Aluminium wire is used to make transmission cables.