The correct option is (a) M=∫Ωcρψ^Tψdx

For explanation I would say: The vector form of the finite element model in the flow domain is , MΔ+K^11Δ+K^12P=F^1 where F is force matrix, M is a mass matrix, K^11 is related to velocity term, K^12 is related to the pressure term, P is the pressure matrix, and Δ is the velocity matrix. M is a mass matrix as it contains the mass density values of elements, thus M=∫Ωcρψ^Tψdx, where ρ denotes the mass density.