ANS:D - all the above.

1. Within the flange: In a T-beam, the flange refers to the horizontal top part of the T-shaped cross-section. The neutral axis of a T-beam typically lies within the flange, especially if the flange is wider and contributes significantly to resisting bending stresses. This is because the flange carries a portion of the bending moment and therefore experiences tensile and compressive stresses. The neutral axis divides the section into the compression zone (usually in the flange) and the tension zone (usually in the web). When the flange is relatively wide and provides substantial resistance to bending, the neutral axis tends to be closer to or within the flange.
2. At the bottom edge of the slab: The bottom edge of the slab is typically part of the compression zone of the T-beam, especially if it is reinforced to resist compression. However, the exact location of the neutral axis is not necessarily at the bottom edge of the slab. It depends on the relative stiffness and contribution of the flange and the web to resisting bending stresses. While the bottom edge of the slab may be in the compression zone, the neutral axis may be located above or below it, depending on the specific geometry and loading conditions of the T-beam.
3. Below the slab: The neutral axis is usually not below the slab, as this would imply that the entire section is in compression, which is unlikely for a T-beam. The neutral axis divides the section into compression and tension zones, and it is typically located within the flange or in the vicinity of the flange-web junction. While the bottom edge of the slab may be part of the compression zone, the neutral axis is typically located above it, within the flange or the flange-web junction.