The stability of the oxidation state in lanthanoid elements depends on which of the following?

Number of paramagnetic ions among the following $d$- and $f$-block metal ions is . . . . . . . $Mn^{2+}$, $Cu^{2+}$, $Zn^{2+}$, $Yb^{2+}$, $Sc^{3+}$, $La^{3+}$, $Gd^{3+}$, $Lu^{3+}$, $Ti^{4+}$, $Ce^{4+}$. (Atomic number of $Mn = 25$, $Cu = 29$, $Zn = 30$, $Yb = 70$, $Sc = 21$, $La = 57$, $Gd = 64$, $Lu = 71$, $Ti = 22$, $Ce = 58$)

In the periodic table,the first transition series is placed in:

Magnetic moment of $Gd^{3+}$ ion $(Z = 64)$ is .......... $B.M.$

Discuss the position of $d$-block elements in the periodic table.

The atomic radius of $Ag$ is closest to