The incorrect order of electronegativity is :

1.	Cl > S > P > Si	2.	Si > Al > Mg > Na
3.	F > Cl > Br > I	4.	None of the above.

Which of the following third-period elements has a positive electron gain enthalpy?

Read the following statements (S) and Explanation (E). Choose the correct answers from the codes (1), (2), (3) and (4):

S : Sulphate is estimated as ${\mathrm{BaSO}}_4$ and not as ${\mathrm{MgSO}}_4$.

E : Ionic radius of ${\mathrm{Mg}}^{2+}$ is smaller than ${\mathrm{Ba}}^{2+}$.

1.  S is correct but E is wrong
2.  S is wrong but E is correct
3.  Both S and E are correct and E is correct explanation of S
4.  Both S and E are correct but E is not correct explanation of S

For the second-period elements, the correct increasing order of first ionisation enthalpy is:

Which one of the following orders is not in accordance with the property stated against?

1. \(\mathrm{F}_2>\mathrm{Cl}_2>\mathrm{Br}_2>\mathrm{I}_2: \text { Oxidising power }\)$$

2. \(\mathrm{Hl}>\mathrm{HBr}>\mathrm{HCl}>\mathrm{HF}: \text { Acidic property in water }\)

3. ${}_{}$\(\mathrm{F_2>C l_2>B r_2>I_2: \text { Electronegativity }}\)

4. ${}_{}$\(\mathrm{F_2>C l_2>B r_2>I_2: \text { Bond dissociation energy }}\)

Identify the correct order of the size of the following:

1. $C{a}^{2+}<K^{+}<Ar<S^{2-}<C{l}^{-}$

2. $C{a}^{2+}<K^{+}<Ar<C{l}^{-}<S^{2-}$

3. $Ar<C{a}^{2+}<K^{+}<C{l}^{-}<S^{2-}$

4. $C{a}^{2+}<A{r}^{+}<K^{+}<C{l}^{-}<S^{2-}$

Among the following, the most characteristic oxidation states for lead and tin are, respectively:

1. +4, +2

2. +2, +4

3. +4, +4

4. +2, +2

Which of the following pairs consists of elements that belong to the same period of the Periodic Table? 

Which of the following ionic species is isoelectronic with \(\mathrm{Be^{2+}}\)?