Magnesium burns in oxygen: 24 g of magnesium combine with 16 g of oxygen to form magnesium oxide. How much magnesium oxide forms when 12 g of magnesium burns completely in excess oxygen?
Answer and explanation
Correct answer: A. 20 g
- Step 1: Mass is conserved: 24 g + 16 g = 40 g of oxide. Step 2. 12 g is half of 24 g, so the oxide is half of 40 g = 20 g. Answer: 20 g. Why not the others: 28 g adds the full 16 g of oxygen, 40 g is for 24 g of magnesium, and 10 g halves again.
Practise more Science and Technology Reasoning.
Free questions with an explanation for every one, and full timed ENLA Secondary Practice (Peru) mock tests.
More Science and Technology Reasoning questions
- In which part of a plant cell does photosynthesis take place?
- Which are the products of photosynthesis?
- In the food chain grass, grasshopper, frog, snake, the number of frogs falls sharply because of disease. What is the most likely short-term…
- In pea plants, tall (T) is dominant over short (t). Two plants with genotype Tt are crossed. What is the probability that an offspring is sh…
- What is the main function of red blood cells?
- Which of these organisms is a producer in a lake ecosystem?