7. The full symbol of an ion of an element is 39X+? Which one of the following is the number of electrons in the ion? A. 18 B. 19 C. 20 D. 39 8. The atomic numbers of elements W, X, Y and Z are 9, 11, 18 and 20 respectively. Which one of the elements shows similar properties as an element with atomic number 10? A. W B. X C. D. 9. Y Z Element Y forms acidic oxide and reacts with hydrogen to form hydride with the formula YH3. To which one of the following groups in the periodic table does Y belong A. I B. III C. V D. VII 10. A. Which of the elements does not react with chlorine? Aluminium B. Oxygen C. Sodium D. Argon