NJC_2025_H2_Chemistry_Prelim_P1_Ans

NJC/H2 Chem Prelim/01/2025 [Turn over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 1 Multiple Choice Additional Materials: Optical Answer Sheet Data Booklet 9729/01 23 September 2025 1 hour READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, highlighters, glue or correction fluid. Write your name, subject class and registration number on the Answer Sheet in the spaces provided unless this has been done for you. There are thirty questions on this paper. Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the separate Answer Sheet. Read the instructions on the Answer Sheet very carefully. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet. The use of an approved scientific calculator is expected, where appropriate. Instructions on how to fill in the Optical Mark Sheet Shade the index number in a 5 digit format on the optical mark sheet: 2nd digit and the last 4 digits of the Registration Number. Example: Student Examples of Registration No. Shade: 2405648 45648 This document consists of 16 printed pages.

2 NJC/H2 Chem Prelim/01/2025

3 NJC/H2 Chem Prelim/01/2025 [Turn over Answer Key for P1 (MCQ) 1 A 6 C 11 C 16 C 21 C 26 D 2 D 7 C 12 C 17 B 22 A 27 C 3 A 8 C 13 B 18 D 23 D 28 C 4 B 9 B 14 B 19 C 24 C 29 C 5 B 10 D 15 A 20 C 25 C 30 A 1 Sodium chromate(VI), Na2CrO4, is manufactured by heating chromite, FeCr2O4, with sodium carbonate in an oxidising atmosphere. Chromite contains Cr2O42– ions. 4FeCr2O4 + 8Na2CO3 + 7O2 ⎯→ 8Na2CrO4 + 2Fe2O3 + 8CO2 What happens in this reaction? A Chromium and iron are the only elements oxidised. B Chromium, iron and carbon are oxidised. C Only chromium is oxidised. D Only iron is oxidised. Ans: A Reactants: FeCr₂O4 (Fe = +2 and Cr = +3), Na2CO3 (C = +4), O2 (O = 0). Products: Fe₂O₃ (Fe = +3), Na₂CrO₄ (Cr = +6), CO₂ (C = +4). Changes: Fe: +2 → +3 (oxidised) Cr: +3 → +6 (oxidised) C: +4 → +4 (no change) O: 0 → –2 (reduced) So, only Fe and Cr are oxidised. 2 Which species has two unpaired electrons? A B+ B Cu+ C Mg D S Ans: D B+: 1s2 2s2 No unpaired electrons Cu+: 1s2 2s2 2p6 3s2 3p6 3d10 No unpaired electrons Mg: 1s2 2s2 2p6 3s2 No unpaired electrons S: 1s2 2s2 2p6 3s2 3p4 2 unpaired 3p electrons

4 NJC/H2 Chem Prelim/01/2025 3 The variation in the second ionisation energy of eight consecutive elements in the Periodic Table with atomic numbers ≤ 20 is shown in the graph. Which element is a Group 13 element? Ans: A The large drop in 2 nd I.E. shows that D+ ion has the ns 1 electronic configuration.