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The atomic number of phosphorus, sulphur and potassium are 15, 16 and 19 respectively.
The formulae of their ions are# P^(3-#, #S^(2-# and #K^(+#. These ions have the same number of electrons.
(a) Write the electron arrangement of the ions
(b) Arrange the ions in the order of increasing ionic radius starting with smallest. Give a reason for the order.