Q.Which of the following sets of ions contain only paramagnetic ions
a. Sm3⊕, Ho3⊕, Lu3⊕
b. La3⊕, Ce3⊕, Sm3⊕
c. La3⊕, Eu3⊕, Gd3⊕
d. Ce3⊕, Eu3⊕, Yb3⊕

Step 1. Recall which f-electron counts give zero unpaired electrons. f0 (e.g. La3+) and f14 (e.g. Lu3+) are the only fully-empty or fully-paired-up f configurations, so ions with these counts are diamagnetic; every other f-electron count (f1 through f13) leaves at least one unpaired electron and is paramagnetic.

Step 2. Check option (a): Sm3+(f5), Ho3+(f10), Lu3+(f14). Lu3+ is f14 -- diamagnetic. This set fails (not all paramagnetic).

Step 3. Check option (b): La3+(f0), Ce3+(f1), Sm3+(f5). La3+ is f0 -- diamagnetic. Fails. …

Testing each option's three ions against Table 8.13's f-electron/unpaired-electron data, eliminating any …

• Assuming any Ln3+ ion is automatically paramagnetic just because lanthanoids are described as 'strongly paramagnetic' in Section 8.12 -- that description is about the SERIES as a whole; the f0 (La3+) and f14 (Lu3+) end members are genuine except …