The number of element from the following that do not belong to lanthanoids is $\mathrm{Eu}, \mathrm{Cm}, \mathrm{Er}, \mathrm{Tb}, \mathrm{Yb}$ and $\mathrm{Lu}$

<p>To determine the number of elements from the given list that do not belong to the lanthanoids, let's first define what lanthanoids are. The lanthanoids consist of the 15 chemical elements in the periodic table from Lanthanum ($\mathrm{La}$) with atomic number 57 to Lutetium ($\mathrm{Lu}$) with atomic number 71. Thus, lanthanoids include:</p> <ul> <li>Lanthanum ($\mathrm{La}$)</li> <li>Cerium ($\mathrm{Ce}$)</li> <li>Praseodymium ($\mathrm{Pr}$)</li> <li>Neodymium ($\mathrm{Nd}$)</li> <li>Promethium ($\mathrm{Pm}$)</li> <li>Samarium ($\mathrm{Sm}$)</li> <li>Europium ($\mathrm{Eu}$)</li> <li>Gadolinium ($\mathrm{Gd}$)</li> <li>Terbium ($\mathrm{Tb}$)</li> <li>Dysprosium ($\mathrm{Dy}$)</li> <li>Holmium ($\mathrm{Ho}$)</li> <li>Erbium ($\mathrm{Er}$)</li> <li>Thulium ($\mathrm{Tm}$)</li> <li>Ytterbium ($\mathrm{Yb}$)</li> <li>Lutetium ($\mathrm{Lu}$)</li> </ul> <p>Given the list of elements: <b>Eu</b> (Europium), <b>Cm</b> (Curium), <b>Er</b> (Erbium), <b>Tb</b> (Terbium), <b>Yb</b> (Ytterbium), and <b>Lu</b> (Lutetium), we can now check which of these are not part of the lanthanoids:</p> <ul> <li>$\mathrm{Eu}$ (Europium) <b>belongs</b> to the lanthanoids.</li> <li>$\mathrm{Cm}$ (Curium) <b>does not belong</b> to the lanthanoids; it is an actinoid.</li> <li>$\mathrm{Er}$ (Erbium) <b>belongs</b> to the lanthanoids.</li> <li>$\mathrm{Tb}$ (Terbium) <b>belongs</b> to the lanthanoids.</li> <li>$\mathrm{Yb}$ (Ytterbium) <b>belongs</b> to the lanthanoids.</li> <li>$\mathrm{Lu}$ (Lutetium) <b>belongs</b> to the lanthanoids.</li> </ul> <p>From the given list, only <b>Cm</b> (Curium) does not belong to the lanthanoids, which means the correct answer is:</p> <p>Option B: 1</p>