This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “P-Block – Group 17 Elements”.
1. Group 17 elements are also called halogens.
Explanation: Group 17 elements are called halogens. The name halogen (Greek, halo = sea salts, genes = producing) meaning sea salt formers was given to them by Schweigger in 1811 because the salts (chlorides, bromides and iodides) of the first three elements occur in sea water.
2. Which of the following element is most reactive?
Explanation: Of all the halogens, fluorine is the most reactive and hence is also called super halogen. Fluorine is also the most electronegative (EN = 4.0) element in the periodic table. This indicates that fluorine has a high tendency to gain electrons from other elements with lower electronegativities.
3. Which of the following halogen is radioactive?
Explanation: Astatine (Atomic No. = 85, Symbol-At) is radioactive and hence occurs in nature only in traces. Therefore, not much is known about its chemistry, though it might be expected to be a metalloid.
4. Halogens do not occur in the free state.
Explanation: Halogens are highly reactive elements and hence do not occur in the free state or native state. They mainly occur in the combined state in the form of their halide (X–) salts although iodine also occurs as iodate (IO3–).
5. Which of the following is not a mineral of fluorine?
Explanation: Fluorine occurs as insoluble fluorides to the extent of 0.07% in the earth’s crust. The chief minerals of fluorine are:
- Fluorspar, CaF2
- Cryolite, Na3AlF6
- Fluoroapatite, CaF2.3Ca3(PO4)2
6. What is the general electronic configuration of the halogens?
Explanation: The elements of group 17 have seven electrons in the valence shell and hence their general electronic configuration is ns2np5, i.e., ns2npx2npy2npz1 where n = 2-6. Thus, they contain one electron less than the nearest inert gas configuration.
7. What is the correct order of enthalpy of dissociation of halogens?
a) F2 > Cl2 > Br2 > I2
b) Cl2 > Br2 > F2 > I2
c) Cl2 > F2 > Br2 > I2
d) F2 > Br2 > Cl2 > I2
Explanation: Enthalpy of dissociation decreases as the bond distance increases from F2 to I2 due to a corresponding increase in the size of the atom as we move down the group from F to I. The F-F bond dissociation enthalpy is, however, smaller than that of Cl-Cl and even smaller than that of Br-Br. This is due to the reason that F atom is very small and hence the electron-electron repulsions between the lone pairs of electrons are very large.
8. What is the atomicity of halogens?
Explanation: Each halogen has one electron less than the nearest inert gas. As a result, halogens are very reactive elements. They readily share their single unpaired electron with other atoms to form covalent bonds. Thus, all halogens exist as diatomic molecules.
9. Who discovered the element chlorine?
a) Joseph Priestley
b) Antoine Lavoisier
c) Humphry Davy
d) Wilhelm Scheele
Explanation: Chlorine was discovered in 1774 by Carl Wilhelm Scheele by heating HCl with MnO2. In 1810, Davy established its elementary nature and suggested the name chlorine on the basis of its colour (Greek, chloros = greenish yellow).
10. Which of the following halogen exists as a solid at room temperature?
Explanation: The strength of the van der Waals between molecules forces increases as the size of the halogen increases from fluorine to iodine. As a result, F2 and Cl2 are gases at room temperature, Br2 is a liquid whereas I2 is a solid.
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