The atomic number of the element present in the 3rd period and 17th group of the periodic table would be:

1.	18	2.	23
3.	24	4.	17

The similarity in physical and chemical properties in a group of periodic table is due to the:

1. Same atomic number

2. Same number of valence electrons

3. Same atomic mass

4. Same number of isotopes

The ionic radius indicates the distance between the nucleus and:

1. Outermost shell of an atom.

2. Outermost shell of an ion.

3. Outermost shell of the cation only.

4. Outermost shell of the anion only.

 The trend of atomic radius in a period and a group is :

Anions are larger in radius than their parent atoms because:

The energy of an electron in the ground state of the hydrogen atom is $–2.18\times {10}^{-18}J$.  The ionization enthalpy of atomic hydrogen in terms of J ${\mathrm{mol}}^{-1}$ is:

1. 2.81 × 10⁶ J mol${}^{-1}$

2. 1.31 × 10⁶ J mol${}^{-1}$

3. 2.31 × 10⁶ J mol${}^{-1}$

4. 1.81 × 10⁶ J mol${}^{-1}$

The explanation for the fact that the first ionization enthalpy of sodium is lower than that of magnesium but its second ionization enthalpy is higher than that of magnesium would be :

 The ionization enthalpy of the main group elements tends to decrease down a group due to, 

1) Increase in the atomic size of elements and increase in the shielding effect

2) Decrease in the atomic size of elements and increase in the shielding effect

3) Increase in the atomic size of elements and decrease in the shielding effect

4) Decrease in the atomic size of elements and decrease in the shielding effect

The first ionization enthalpy values (in kJ mol^–1) of group 13 elements are :

The explanation for the deviation from the general trend can be -

1. Ga has lower ionization enthalpy than Al.

2. Ga has higher ionization enthalpy than Al.

3. Al has higher ionization enthalpy than Ga. 

4. Ga has a lesser valence electron than Al.

An element with higher negative electron gain enthalpy in the given pair is:

(i) O or F  (ii) F or Cl
1. O, Cl
2. F, F
3. O, F
4. F, Cl