JEE Main · 2025 · 04 Apr 2025 · Shift 2 · Modern Physics

The parent $P$ has no source and only decays, so its mass falls exponentially from the start. The intermediate $Q$ is produced by the decay of $P$ and itself decays into $R$, so its mass first grows, reaches a maximum, and then declines. The final product $R$ is stable and only accumulates, so its mass rises steadily and tends towards the initial mass of $P$. The correct graph is the one showing $P$ decaying exponentially, $Q$ rising to a peak and then falling, and $R$ increasing to a saturation value.