Which words are to be recited aloud and which are to be recited silently in the obligatory prayers?

The ruling on vocalizing (Jahr) andخفض الصوت (Israr) in prayer for the Imam, the one praying behind him (Ma'mum), and the individual praying alone (Munfarid) is as follows:

1. It is sunnah for the Imam to vocalize the Takbirat al-Ihram (opening takbir). The munfarid and the ma'mum should say it silently according to most scholars. 2. It is sunnah for the Imam to vocalize the recitation of Al-Fatihah and whatever else is easy (of the Quran) in the Fajr prayer and in the first two rak'ahs of the Maghrib and Isha prayers. It is permissible for them (the Imam and munfarid) to vocalize some verses in a silent prayer. The ma'mum does not vocalize behind his Imam. 3. It is sunnah for the Imam to vocalize the takbirat al-intiqal (takbirs of transition) and the saying: " Sami' Allahu liman hamidah " (Allah hears the one who praises Him). Whereas, it is sunnah for the ma'mum and the munfarid to say them silently, unless there is a need to convey the Imam's takbir to the ma'mums. 4. It is sunnah to vocalize the ta'min (saying Ameen) in vocal prayers for the Imam, the ma'mum, and the munfarid according to the majority of scholars. 5. It is sunnah for the Imam to vocalize the Qunut, and for the ma'mum to say Ameen to it. As for the munfarid, some say he should say it silently, while others give him the choice between vocalizing and saying it silently. 6. It is sunnah for the Imam to vocalize the taslim (salutation) to exit the prayer.

It is worth noting the scholars' differing opinions on the definition of jahr and israr. Israr is defined as the worshiper making himself hear, or moving the tongue and lips. Jahr is making others hear, and there is no upper limit to its volume.