Which among the following lanthanoids shows only $+3$ oxidation state?

Lanthanoid ions with $4f^7$ configuration are :
$A$. $Eu^{2+}$
$B$. $Gd^{3+}$
$C$. $Eu^{3+}$
$D$. $Tb^{3+}$
$E$. $Sm^{2+}$
Choose the correct answer from the options given below :

Number of colourless lanthanoid ions among the following is . . . . .
$Eu^{3+}, Lu^{3+}, Nd^{3+}, La^{3+}, Sm^{3+}$

Which of the following lanthanoids exhibits no effective magnetic moment in the $+3$ oxidation state?

Which lanthanoid from the following has the highest first ionisation enthalpy $(IE_1)$?

Which of the following is a lanthanoid element?