$2.$ Click PC$0$ to open its properties and click the Desktop tab. Click IP Configuration.

$3.$ In the IP Address text box, type $192\mathrm{.}168\mathrm{.}100\mathrm{.}0$ as IPv$4$ Address and $255\mathrm{.}255\mathrm{.}255\mathrm{.}0$ as Subnet Mask $,$ and press Enter. You see an error message stating that the IP address and subnet mask combination is invalid. Explain why.