The atomic number of sodium is 11. So, neutral sodium atom has 11 electrons and its electronic configuration is 2, 8, 1. But \(Na^+\) has 10 electrons. Out of 10, K-shell contains 2 and L-shell 8 electrons respectively. Thus, \(Na^+\) has completely filled K and L shells.
In Fig. 9.26, A, B, C and D are four points on a circle. AC and BD intersect at a point E such that ∠ BEC = 130° and ∠ ECD = 20°. Find ∠ BAC.