Lanthanoid ions with $4 \mathrm{f}^7$ configuration are :

(A) $\mathrm{Eu}^{2+}$

(B) $\mathrm{Gd}^{3+}$

(C) $\mathrm{Eu}^{3+}$

(D) $\mathrm{Tb}^{3+}$

(E) $ \mathrm{Sm}^{2+}$

Choose the correct answer from the options given below :

The incorrect statements regarding geometrical isomerism are :

(A) Propene shows geometrical isomerism.

(B) Trans isomer has identical atoms/groups on the opposite sides of the double bond.

(C) Cis-but-2-ene has higher dipole moment than trans-but-2-ene.

(D) 2-methylbut-2-ene shows two geometrical isomers.

(E) Trans-isomer has lower melting point than cis isomer.

Choose the correct answer from the options given below :

Given below are two statements :

Statement I : One mole of propyne reacts with excess of sodium to liberate half a mole of $\mathrm{H}_2$ gas.

Statement II : Four g of propyne reacts with $\mathrm{NaNH}_2$ to liberate $\mathrm{NH}_3$ gas which occupies 224 mL at STP.

In the light of the above statements, choose the most appropriate answer from the options given below :

Which of the following electronegativity order is incorrect?