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Following statements related to radioactivity are given below: (a) Radioactivity is a random and spontaneous process and is dependent on physical and chemical conditions. (b) The number of un-decayed nuclei in the radioactive sample decays exponentially with time. (c) Slope of the graph of log e (no. of undecayed nuclei) Vs. time represents the reciprocal of mean life time ( τ ). (d) Product of decay constant ( λ ) and half-life time (T 1/2 ) is not constant. Choose the most appropriate answer from the options given below:

1. (a) and (b) only
2. (b) and (d) only
3. (b) and (c) only
4. (c) and (d) only

Correct answer: (b) and (c) only

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