19. The following diagram is the electron diagram of the compound formed between elements X and Y (showing electrons in the outermost shell only): Which of the following combinations is correct? A.B.C.D.ElementXGroupIVGroupVGroupIGroupIVElementYGroupVIIGroupVIIGroupVIGroupVI 20. Which of the following are intermolecular forces? (1) Van der Waals' forces (2) Hydrogen bonding (3) Electrostatic forces between ions A. (1) and (2) only B. (1) and (3) only C. (2) and (3) only D. (1), (2) and (3) 21. What is the relative molecular mass of carbon dioxide? (Relative atomic masses of C=12.0,O=16.0 ) A. 28.0 B. 44.0 C. 60.0 D. 74.0 22. What are the numbers of lone pairs and bond pairs of electrons of a PH3 molecule? 23. Which of the following statements best describes the general trend of electronegativity in the Periodic Table? A. Electronegativity increases down a group and from left to right across a period. B. Electronegativity increases down a group and decreases from left to right across a period. C. Electronegativity decreases down a group and from left to right across a period. D. Electronegativity decreases down a group and increases from left to right across a period. 24. Which of the following bonds do you think would be the most polar? A. HF B. HN C. HCl D. HO