The answer to the question of where is the Option key is simple. The Option key on a Mac is the same as the Alt key in Windows. Otherwise known as the Alternate key, it’s most commonly represent by the symbol second from left in the photo at right, especially on Apple Mac keyboards. But it may also be seen in its inverted form.
Apple removed the Option naming convention on non-US Mac keyboards around the time of the processor migration from Motorola/IBM to Intel; i.e., after leaving the G3, G4 and G5 for the Intel Core 2 Duo and Core i3/i5/i7 series.
The Alt key will be more familiar to Windows PC users as the key immediately to the left of the Spacebar. So if you plug a Windows or IBM PC keyboard into a Mac, pressing the Alt key has the same effect as pressing the Option key.
The Option key has many essential uses on the Mac; notably to select boot partition when starting the computer, and for direct printing of diacritical marks such as å, ß, ∂ and µ from the keyboard. It is also important for keyboard shortcut commands.