(a) State whether the following statements are True or False. Justify your answer.

(1) Fluorine is most electronegative element.

(2) The size of potassium atom is greater than the size of sodium atom.

(b) Calculate the number of moles in 9 grams of water.

(a) (1) True
Reason — Fluorine is placed in period 2 group 17 (VIIA) in the modern periodic table i.e., it occupies the upper right hand corner of the periodic table. Along a period from left to right electronegativity increases and down a group from top to bottom it decreases. Hence, Fluorine being the topmost and rightmost element in its group and period is the most electronegative element of the periodic table.

(2) True
Reason — Atomic size increases on moving down the group. As potassium lies below sodium in its group, hence, size of potassium atom is greater than the size of sodium atom.

(b) Molar mass of water [H₂O] = 2(1) + 16 = 18

Number of moles = $\dfrac{\text{Given mass}}{\text{Molar mass}}$ = $\dfrac{9}{18}$ = 0.5 moles

Hence, 0.5 moles are present in 9 gm of water.