Question

Which of the following substances do not have standard enthalpy of formation as zero?

• A. $Ca\left(s\right)$
• B. $Hg\left(l\right)$
• C. $O_2\left(g\right)$
• D. $C{O}_2\left(g\right)$

Answer 1

The correct option is D $C{O}_2\left(g\right)$

Standard enthalpy of formation of elements in pure state at 298 K and 1 bar is zero.
$Ca\left(s\right),Hg\left(l\right),O_2\left(g\right)$ are in their standard states so standard enthalpy of formation is zero