What is madd al-farq? How is it pronounced? Is it one of the types of mandatory contiguous madd (madd wajib muttasil)?

The 'madd al-farq' (distinguishing prolongation) is the madd that occurs after the hamzat al-istifham (interrogative hamza). Examples of it in the Qur’an include: ﴿ءاللهُ أَذِنَ لَكُمْ﴾ (Has Allah permitted you?), ﴿آلْآنَ وَقَدْ عَصَيْتَ﴾ (Now! While you had disobeyed?), and ﴿آلْآنَ وَقَدْ كُنْتُمْ بِهِ تَسْتَعْجِلُونَ﴾ (Now! While you were impatient for it?). It is a type of 'madd lazim' (necessary prolongation) according to those who consider the hamzat al-wasl (connecting hamza) as a madd for the hamzat al-istifham. It is named thus to distinguish between the interrogative hamza and the declarative hamza.