Quantum Key Distribution (QKD) protocols such as Bennett and Brassard protocol (BB84) are widely regarded as unconditionally secure. However, practical implementations of BB84 face vulnerabilities against multiple attack strategies, including Photon Number Splitting (PNS) attacks, intercept-resend attacks, basis-reconciliation leakage, and side-channel intensity-monitoring attacks. To address these limitations, we propose an Index-Grouped Quantum Key Distribution (IG-QKD), a grouped-photon modification of the BB84 protocol. In IG-QKD, each logical bit is encoded using n polarized photons instead of a single photon. The receiver measures each group on a single random basis, and correctness is determined without revealing the basis; only indices of successful matches are announced. This eliminates the conventional weakness exploited during basis disclosure and inherently prevents PNS attacks by ensuring that a subset of photons yields negligible information. In addition, the grouped-photon design enables an intensity-threshold monitoring mechanism, where any attempt by an eavesdropper (Eve) to intercept or siphon photons, causes detectable deviations from calibrated intensity levels, allowing reliable eavesdropper detection even in noisy or lossy channels. We obtain the key length for given total number of bits transmitted (N) and the group size (n) as \(K\sim N/2n\) , which is followed by our simulation results. Our simulations show that the proposed method strengthens resilience not only against PNS attacks but also against intercept-resend, man-in-the-middle, and side-channel intensity attacks, while improving tolerance to photon loss and channel noise. Additionally, the results demonstrate that IG-QKD provides a more comprehensive defense against major attack strategies targeting BB84, offering enhanced security, scalability, and compatibility with existing hardware for real-world quantum communication networks.