How many orbitals contain one or more electrons in an isolated ground state iron atom (Z = 26)?

There are 15 orbitals contain one or more electrons in an isolated ground state iron atom (Z = 26)

${\mathrm{Fe}}_{26}=1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{2}3{\mathrm{d}}^6$

The number of the orbital in $1\mathrm{s},2\mathrm{s},2\mathrm{p},3\mathrm{s},3\mathrm{p},4\mathrm{s},3\mathrm{d}$are $1,1,3,1,3,1,5$ 

The sum of the orbitals are,

$$\begin{gathered} =1+1+3+1+3+1+5 \\ =15 \end{gathered}$$

Hence, option C is correct.