Question

1. which best describes a covalent bond?

(a) complete even sharing of electrons
(b) movement of electrons to a metal
(c) sharing of electrons between two atoms
(d) has a partially positive charge
(e) none of the above describes a covalent bond.

1. which of the following phrases best describes the term solution?

(a) a heterogeneous mixture of two or more substances
(b) a homogeneous mixture of two or more substances
(c) a mixture of two or more liquids where a physical separation can be seen
(d) any chemical compound dissolved in water
(e) the answer to a question

1. the lowest whole number coefficient of o₂(g) in the balanced equation of

c₅h₁₂(g) + o₂(g) → co₂(g) + h₂o(g) is
(a) 1 (b) 5 (c) 8 (d) 18 (e) n/a

1. the mass number of any element is defined as ...

(a) the number of protons and electrons (c) the number of protons and neutrons
(b) the average atomic mass of that element (d) the number of protons only

1. the number of electrons in the nitride ion (n³⁻) is

(a) 4 (b) 7 (c) 10 (d) 14

1. the number of valence electrons in the element barium (#56) is

(a) 2 (b) 4 (c) 6 (d) 8

1. the reaction 2 al(s) + fe₂o₃(s) → 2 fe(l) + al₂o₃(s) produces molten iron from connecting railway tracks. this reaction is classified as:

(a) a decomposition (c) a synthesis
(b) a single displacement (d) a double displacement

1. when hydrocarbons react with oxygen to produce carbon dioxide and water the reaction is known as:

(a) cracking (c) reforming
(b) combustion (d) distillation

1. the law of conservation of mass states that:

(a) there are four elements: earth, air, fire, water

Explanation:

• Question 20: A covalent bond is defined as the sharing of electrons between two atoms. Option (C) correctly describes this.
• Question 21: A solution is a homogeneous mixture of two or more substances. Option (B) is correct.
• Question 22: For the combustion of \(C_5H_{12}\):
• The unbalanced equation is \(C_5H_{12}(g)+O_2(g)\to CO_2(g)+H_2O(g)\).
• Balance carbon: \(C_5H_{12}(g)+O_2(g)\to 5CO_2(g)+H_2O(g)\).
• Balance hydrogen: \(C_5H_{12}(g)+O_2(g)\to 5CO_2(g)+6H_2O(g)\).
• Balance oxygen: \(C_5H_{12}(g)+8O_2(g)\to 5CO_2(g)+6H_2O(g)\). So the coefficient of \(O_2\) is 8 (Option C).
• Question 23: The mass number of an element is the number of protons and neutrons. Option (C) is correct.
• Question 24: Nitrogen (\(N\)) has atomic number 7 (7 protons). The nitride ion \(N^{3 -}\) has \(7 + 3=10\) electrons. Option (C) is correct.
• Question 25: Barium (\(Ba\)) is in group 2. Elements in group 2 have 2 valence electrons. Option (A) is correct.
• Question 26: The reaction \(2Al(s)+Fe_2O_3(s)\to 2Fe(l)+Al_2O_3(s)\) is a single - displacement reaction (one element replaces another in a compound). Option (B) is correct.
• Question 27: When hydrocarbons react with oxygen to produce carbon dioxide and water, it is called combustion. Option (B) is correct.
• Question 28: The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction. None of the options (A - D) correctly state the law. But if we assume it's a mis - keyed question and we consider basic knowledge, the law is about mass conservation, not the four elements.

Answer:

• Question 20: C. sharing of electrons between two atoms
• Question 21: B. a homogeneous mixture of two or more substances
• Question 22: C. 8
• Question 23: C. the number of protons and neutrons
• Question 24: C. 10
• Question 25: A. 2
• Question 26: B. a single displacement
• Question 27: B. combustion
• Question 28: None of the options correctly state the Law of Conservation of Mass. But if we assume it's about mass conservation concept (not the four - element option A), the law is not correctly represented by the given options. However, if forced to choose based on common knowledge (ignoring option A's incorrectness about four elements), we can say that the law is mis - represented here. But in a proper sense, the law is that mass is conserved in chemical reactions.