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 \( ( \tau ) \).
(\( d \)) Product of decay constant \( ( \lambda ) \) and half-life time \( ( T_{1/2} ) \) is not constant.
Choose the most appropriate answer from the options given below:
