Arsenic forms a compound with fluorine. In this compound, the arsenic atom has no lone pair of electrons and there are no dative bonds. Selenium also forms a compound with fluorine. In this compound, the selenium atom has no lone pair of electrons and there are no dative bonds. In which compounds are there two different bond angles? (In this question, 180° bond angles should be ignored.)
▶️ Answer/Explanation
Ans: B
Arsenic fluoride (AsF5) has a trigonal bipyramidal shape with two distinct bond angles (90° and 120°). Selenium fluoride (SeF6) has an octahedral shape with only one bond angle (90°). Since the question ignores 180° angles, only arsenic fluoride has two different bond angles, making B the correct answer.
A structure for borazole, N₃B₃H₆, is shown.
Which shape is borazole and how many π electrons are there in the structure? 
▶️ Answer/Explanation
Ans: D
Borazole (N₃B₃H₆) has a trigonal planar shape due to the alternating boron and nitrogen atoms forming a hexagonal ring with 120° bond angles. The structure is aromatic, containing 6 π electrons (3 from nitrogen lone pairs and 3 from boron-nitrogen π bonds). Thus, the correct option is D (trigonal planar, 6 π electrons).
Glauber’s salt consists of crystals of hydrated sodium sulfate, Na₂SO₄•xH₂O, which can be used for the manufacture of detergents. When a sample of Glauber’s salt was heated, 1.91 g of water was removed leaving 1.51 g of anhydrous Na₂SO₄. What is the value of x in Na₂SO₄•xH₂O?
▶️ Answer/Explanation
Ans: C
To find \( x \) in Na₂SO₄•xH₂O, we calculate the moles of anhydrous Na₂SO₄ and water. The molar mass of Na₂SO₄ is \( 142 \, \text{g/mol} \), so moles of Na₂SO₄ = \( \frac{1.51 \, \text{g}}{142 \, \text{g/mol}} = 0.0106 \, \text{mol} \). The moles of H₂O = \( \frac{1.91 \, \text{g}}{18 \, \text{g/mol}} = 0.106 \, \text{mol} \). The ratio \( \frac{0.106}{0.0106} = 10 \), confirming \( x = 10 \).
7.5 g of nitrogen monoxide reacts with 7.0 g of carbon monoxide on the surface of the catalytic converter in the exhaust system of a car. What is the total volume of the product gases measured at room conditions?
▶️ Answer/Explanation
Ans: C
The reaction is \(2NO + 2CO \rightarrow N_2 + 2CO_2\). Moles of NO = \(\frac{7.5}{30} = 0.25\) mol, and moles of CO = \(\frac{7.0}{28} = 0.25\) mol. Since the reaction consumes equal moles of NO and CO, all reactants are fully converted. The products are \(0.125\) mol \(N_2\) and \(0.25\) mol \(CO_2\), totaling \(0.375\) mol. At room conditions, 1 mol of gas occupies 24 dm³, so total volume = \(0.375 \times 24 = 9.0\) dm³.