Metal deficiency defect is shown by ${\mathrm{Fe}}_{0.93}\mathrm{O}$ .In the crystal , some ${\mathrm{Fe}}^{+2}$ cations are missing and loss of positive charge is compensated by the presence of ${\mathrm{Fe}}^{+3}$ ions . The percentage of  ${\mathrm{Fe}}^{+2}$ ions in the  ${\mathrm{Fe}}_{0.93}\mathrm{O}$ crystals is-