IGCSE Chemistry Paper-1: Specimen Questions with Answers 49 - 50 of 99
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Question 49
Question
MCQ▾Which two gases are formed when electrolysis of water is carried out?
Choices
| Choice (4) | |
|---|---|
a. | Hydrogen and Oxygen |
b. | Oxygen and nitrogen |
c. | Hydrogen and Nitrogen |
d. | Hydrogen and Carbon di oxide |
Answer
a.Explanation
Water ionises to produce hydrogen (H + ) ions and hydroxide (OH¯) ions. These are often displaced from solution to give hydrogen gas and oxygen gas. The substance formed at the cathode is usually hydrogen, unless the solution contains copper or silver ions, in which case, copper or silver will form at the cathode.
Question 50
Question
MCQ▾Which among the below is example of double covalent molecular structure?
Choices
| Choice (4) | |
|---|---|
a. |  |
b. |  |
c. |  |
d. | Question does not provide sufficient data or is vague |
Answer
c.Explanation
Double bond is formed by the sharing of two pairs of electrons of the valence shell.
Example: Oxygen molecule (O = O)
The atomic number of oxygen is 8. It requires two electrons to achieve the nearest stable inert gas configuration, which is neon. To achieve this, two oxygen atoms contribute two unpaired electrons to produce two bond pairs. Thus, they share these two electron pairs to form a double bond.