Which element describes two or more normally closed input switches in series?

The element that describes two or more normally closed input switches in series is the NOR gate. In this context, a NOR gate outputs a low signal (0) when any of its inputs are high (1). When you connect normally closed switches in series, the circuit remains closed and conductive until one of the switches opens, which reflects the behavior of a NOR gate.

When both switches are closed, the input to the NOR gate is low, resulting in a high output. If either of the switches opens (which produces a high signal for that input), the output from the NOR gate will go low. This mirrors the functioning of normally closed switches in series, as the circuit is only interrupted when one switch opens.

In contrast, the other options do not accurately describe the behavior of normally closed switches in series: the NOT gate simply inverts an input, the NAND gate outputs a low only if all its inputs are high (which doesn't align with the behavior of normally closed switches in series), and the OR gate outputs high if any input is high, which does not fit the scenario of two normally closed switches in series.