The electron in the \( n^{\text{th}} \) orbit of \( \mathrm{Li^{2+}} \) is excited to \( (n + 1) \) orbit using the radiation of energy \( 1.47 \times 10^{-17} \, \text{J} \) (as shown in the diagram). The value of \( n \) is _______. (Given : \( R_H = 2.18 \times 10^{-18} \, \text{J} \))
