# NEET Physics Nuclei Questions Solved

A radioactive sample is $\mathrm{\alpha }$-emitter with half life 138.6 days is observed by a student to have 2000 disintegration/sec. The number of radioactive nuclei for given activity are
(a) $3.45×{10}^{10}$               (b) $1×{10}^{10}$
(c) $3.45×{10}^{15}$               (d) $2.75×{10}^{11}$