Number of metal ions characterized by flame test among the following is ________.

$$\mathrm{Sr}^{2+}, \mathrm{Ba}^{2+}, \mathrm{Ca}^{2+}, \mathrm{Cu}^{2+}, \mathrm{Zn}^{2+}, \mathrm{Co}^{2+}, \mathrm{Fe}^{2+}$$

Number of spectral lines obtained in $$\mathrm{He}^{+}$$ spectra, when an electron makes transition from fifth excited state to first excited state will be

Total number of species from the following which can undergo disproportionation reaction is ________.

$$\mathrm{H}_2 \mathrm{O}_2, \mathrm{ClO}_3^{-}, \mathrm{P}_4, \mathrm{Cl}_2, \mathrm{Ag}, \mathrm{Cu}^{+1}, \mathrm{~F}_2, \mathrm{NO}_2, \mathrm{K}^{+}$$

Number of geometrical isomers possible for the given structure is/are _________.