A Characterization of Zero Divisors and Topological Divisors of Zero in $C[a,b]$ and ${\mathrm{\ell }}^{\mathrm{\infty }}$

We give a characterization of zero divisors of the ring $C[a,b]\mathrm{.}$ Using the Weierstrass approximation theorem, we completely characterize topological divisors of zero of the Banach algebra $C[a,b]\mathrm{.}$ We also characterize the zero divisors and topological divisors of zero in ${\mathrm{\ell }}^{\mathrm{\infty }}\mathrm{.}$ Further, we show that zero is the only zero divisor in the disk algebra $\mathcal{A}(\mathbb{D})$ and that the class of singular elements in $\mathcal{A}(\mathbb{D})$ properly contains the class of topological divisors of zero. Lastly, we construct a class of topological divisors of zero of $\mathcal{A}(\mathbb{D})$ which are not zero divisors.