YIJC 2025 Prelim P1 Answers (for exchange)_H2 Chem

1 ©YIJC [Turn over YIJC 2025 H2 Chemistry Paper 1 Suggested Solutions 1 2 3 4 5 B D D B B 6 7 8 9 10 B D C B C 11 12 13 14 15 A D B C B 16 17 18 19 20 D C A C C 21 22 23 24 25 D C D C B 26 27 28 29 30 B D C A D 1 Answer: B Negatively charged ions attracted to positive plate, positive ions to negative plate. D must be negatively-charged, while E and F are positively-charged. Angle of deflection is proportional to charge/mass ratio. Since D and E have roughly the same angle of deflection but different polarity, D and E must have roughly the same charge/mass ratio. F has almost double the angle of deflection as E, so the charge/mass ratio of F must be almost double that of E. particles 14N‾ 28Si2+ 14C2+ charge / mass 1/14 2/28 = 1/14 2/14 = 1/7 2 Answer: D The sharp rise between 2 nd and 3rd I.E. shows that there are 2 valence electron s in the outermost shell. Hence G is in Group 2. The outermost electronic configuration is ns2. It cannot be in Period 3 because Mg (Group 2 in Period 3) has only 12 electrons, and so cannot have 13 successive IEs. The next inner quantum shell contains 8 electrons, as seen by the 8 IEs before the next sharp rise. For a d-block element, the next inner quantum shell should contain 3s, 3p and 3d electrons, which would be more than 8. It is not Al as Al has 3 valence electrons.

2 ©YIJC [Turn over 3 Answer: D While alcohols have intermolecular hydrogen bonding between molecules, as the carbon chain length of an alcohol increases, the boiling point increases as the id-id interactions become stronger due to the larger and more polarisable electron cloud. Hydrogen chloride dissociates and releases an H+ that forms dative bond, not hydrogen bond, with water molecules to produce H3O+. CH3CHO has a higher boiling point than CH 3CH2CH3 due to stronger permanent dipole-permanent dipole attraction between CH3CHO molecules, and not intermolecular hydrogen bonding. In ice, each water molecule forms 4 hydrogen bonding with 4 other water molecules. These hydrogen bonds are relatively long , giving rise to an open structure . I n liquid, water molecules aggregate together via hydrogen bonding. Hence, ice has a lower density than water at 0 °C. 4 Answer: B Option 2 is non-polar molecule. AlCl3 is trigonal planar in shape and there is no net dipole moment in the molecule as all the dipole moments cancel out each other. Option 3 is non-polar molecule. CO2 is linear in shape and there is no net dipole moment in the molecule as all the dipole moments cancel out each other. Option 1 and 4 are polar as there is net dipole moment in the molecule. 5 Answer: B Option A is correct as Al is a metal (solid) that conducts electricity. Option B is wrong as Al2O3 is insoluble in water. Option C is correct as Al3+ has high charge density so it can undergo hydrolysis in water to form an acidic solution. Option D is correct as Al2O