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

Colourless lanthanoid ions are those with $$4f^0$$ or $$4f^{14}$$ configurations (no unpaired f-electrons to undergo f-f transitions).

$$Eu^{3+}$$: $$[Xe]4f^6$$ — coloured ✗

$$Lu^{3+}$$: $$[Xe]4f^{14}$$ — colourless ✓

$$Nd^{3+}$$: $$[Xe]4f^3$$ — coloured ✗

$$La^{3+}$$: $$[Xe]4f^0$$ — colourless ✓

$$Sm^{3+}$$: $$[Xe]4f^5$$ — coloured ✗

Number of colourless ions = 2 ($$Lu^{3+}$$ and $$La^{3+}$$).

The answer is $$\boxed{2}$$.