I worked on deep sub-micron, full custom mixed-signal integrated circuits for more than a decade, and I can't pass the first level.

> Wire an NMOS transistor so that when In is 1, the output is pulled to ground (0). When In is 0, the output should be unconnected (Z).

Certainly:

(a) The nMOS has 3 connections: its drain is only connected to the output (no +Vdd supply), it's source is tied to ground, it's gate is tied to the signal input

(b) When the gate (input) is driven high, the nMOS transistor turns "on," connecting the output to the source (which is grounded). This acts as a "pull-down network"

(c) When the gate is driven low, the nMOS turns "off," leaving no connection to the output. This is equivalent to a "high-impedance" / "unconnected" / "Z" output

Fails 1/2 tests

(Edit) - I thought the light grey, thick line on the background grid was a wire from "input" to the transistor's gate. It is not. You need to explicitly add a wire from "input" to gate :\