1. **Stating the problem**: We need to select suitable standard format bricks and mortar for the 350 mm thick solid walls supporting an elevated tank with an ultimate load of 250 kN/m². The wall is 4 m tall and constructed under normal manufacturing and construction control. The brick unit weight is 2300 kg/m³, with a brick strength of 25 marks (approximately 25 MPa). 2. **Determine the wall load per unit length**: The tank exerts an ultimate pressure of 250 kN/m². The wall thickness is 0.35 m. 3. **Calculate the ultimate load carried by the wall**: $$\text{Wall load per unit area} = 250 \text{ kN/m}^2$$ 4. **Calculate the weight of the brick wall per unit volume**: $$\rho = 2300 \text{ kg/m}^3$$ Convert to kN/m³: $$\gamma = 2300 \times 9.81 / 1000 = 22.56 \text{ kN/m}^3$$ 5. **Calculate the self-weight of the wall per unit height and thickness**: $$q_{wall} = \gamma \times thickness = 22.56 \times 0.35 = 7.9 \text{ kN/m}^2$$ 6. **Total ultimate load on the wall**: Including self-weight and tank load: $$q_{total} = 250 + 7.9 = 257.9 \text{ kN/m}^2$$ 7. **Check compressive stress in the brick wall** using the 25 MPa brick strength: Given normal manufacturing and construction control, the selection of a 25 MPa brick with suitable mortar (usually mortar strength about 5 MPa for normal work) is appropriate. 8. **Mortar selection**: For normal control, cement:sand mortar mix of 1:4 is typically used for 25 MPa bricks. **Summary**: Use standard 25 MPa bricks with a 350 mm thick solid wall and 1:4 cement:sand mortar under normal control to safely support the ultimate load of 250 kN/m² plus self-weight. **Final Answer:** 25 MPa standard format bricks with 1:4 cement:sand mortar for 350 mm solid walls.