Law of Radioactive Decay question from MHT CET 2026 (19 May, Shift 2)

In an alpha decay, the daughter nucleus produced is itself unstable and undergoes further decay. If the number of parent and daughter nuclei at time $t$ are $N_p$ and $N_d$ respectively and their decay constants are $\lambda_p$ and $\lambda_d$ respectively. What condition needs to be satisfied in order for $N_d$ to remain constant?