$\begin{array}{1 1}(A)\;200\\(B)\;205\\(C)\;210\\(D)\;215\end{array} $

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We get a chord by joining two points.If P is the number of chords from 21 points then,

$P=C(21,2)=\large\frac{21!}{2!(21-2)!}$

$\Rightarrow \large\frac{21!}{2!19!}$

$\Rightarrow \large\frac{21\times 20(19!)}{2\times 1(19!)}$

$\Rightarrow 21\times 10$

$\Rightarrow 210$ chords

Hence (C) is the correct answer.

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