Explanation

The Second Pillar of Islam is Zakat because the pillars are Shahada, Salat (Namaz), Zakat, Sawm (Fast), and Hajj. Namaz is a pillar but it is the second one listed, not necessarily the 'Second Pillar' in all contexts if referring to the sequence after Shahada. Touheed is the concept of oneness of God, which is part of the first pillar (Shahada). Fasting (Sawm) is the fourth pillar, and Zakat is the third pillar.