Particles of masses \( \mathrm{m}, 2 \mathrm{~m}, 3 \mathrm{~m} \ldots \ldots \ldots . . \mathrm...

Particles of masses \( \mathrm{m}, 2 \mathrm{~m}, 3 \mathrm{~m} \ldots \ldots \ldots . . \mathrm{nm} \) gram are placed on the same line at distances, \( l, 2 l, 3 l, \ldots \ldots \mathrm{nl} \mathrm{cm} \) from a fixed point. The distance of centre of mass of the particles from the fixed point in \( \mathrm{cm} \) is:
a. \( \frac{(2 n+1) l}{3} \)
b. \( \frac{l}{n+1} \)
c. \( \frac{n\left(n^{2}+l\right) l}{2} \)
d. \( \frac{2 l}{n\left(n^{2}+l\right) l} \)