______ is used as a cryogenic agent for carrying out various experiments at low temperatures.

In the following reaction, the oxidation state of $\mathrm{S}$ changes from _________.

${\text{C+2H}}_{\text{2}}{\text{SO}}_{\text{4}}\stackrel{}{\to }{\text{ CO}}_{\text{2}}{\text{ + 2SO}}_{\text{2}}{\text{ + 2H}}_{\text{2}}\text{O}$

The following figure shows the ________ defect.