In which set do all the molecules have all their atoms arranged in one plane?
Correct Answer: \( \boxed{\mathrm{D}} \)
Planar molecules include:
The other options contain non-planar molecules such as \(\mathrm{PH_3}\), \(\mathrm{NH_3}\), or \(\mathrm{C_3H_6}\).
Therefore, the correct answer is (D).
Three bond angles are labelled on the molecule shown.
What is the order of decreasing size of the bond angles \(x\), \(y\) and \(z\)?
| Largest | → | Smallest | |
|---|---|---|---|
| A | \(x\) | \(y\) | \(z\) |
| B | \(x\) | \(z\) | \(y\) |
| C | \(y\) | \(z\) | \(x\) |
| D | \(z\) | \(y\) | \(x\) |
Correct Answer: \( \boxed{\mathrm{C}} \)
Angle \(y\) is around a tetrahedral carbon atom with four bonding pairs, so it is approximately \(109.5^\circ\).
Angle \(z\) is around nitrogen with one lone pair. Lone pair-bond pair repulsion decreases the bond angle to about \(107^\circ\).
Angle \(x\) is around sulfur with two lone pairs. The greater lone pair repulsion decreases the bond angle further, making it the smallest.
Therefore, the order of decreasing bond angle is \(y>z>x\), so the correct answer is (C).
When dry ammonia and hydrogen chloride gases are mixed, a solid white ionic compound is formed.
Two statements are listed.
1 The formation of the ionic compound is a redox reaction.
2 During the formation of the ionic compound, the H–N–H bond angle increases.
Which statements are correct?
Correct Answer: \( \boxed{\mathrm{C}} \)
The reaction is:
\(\mathrm{NH_3(g)+HCl(g)\rightarrow NH_4Cl(s)}\)
This is an acid-base reaction, not a redox reaction, because the oxidation states of all atoms remain unchanged.
In \(\mathrm{NH_3}\), the nitrogen atom has one lone pair, giving a trigonal pyramidal shape with an H–N–H bond angle of about \(107^\circ\).
When \(\mathrm{NH_4^+}\) forms, the lone pair is used to form a coordinate bond with \(\mathrm{H^+}\). The ion becomes tetrahedral with bond angles of \(109.5^\circ\).
Therefore, the H–N–H bond angle increases during the reaction.
Therefore, only statement 2 is correct, so the correct answer is (C).
