Modular bricks as per Indian Standards (actual size) According to Indian Standards (IS) for modular bricks, identify the actual size of a modular brick (excluding mortar thickness).

Introduction / Context:
In building materials and construction, it is essential to distinguish between the actual (unit) size of bricks and their nominal size (which includes mortar allowance). Modular sizes are standardised in India to ensure uniform coursing, proper bonding, and predictable masonry dimensions.

Given Data / Assumptions:

• The question asks for the actual size of a modular brick.
• Actual size excludes the mortar thickness.
• Nominal size includes the standard mortar joint thickness for coursing.

Concept / Approach:
Modular brick sizes are specified in IS standards. The actual size is the physical size of the fired brick itself. The nominal size is larger because a standard mortar joint is added in design calculations to achieve modular coordination in masonry.

Step-by-Step Solution:

Verification / Alternative check:
Cross-check with standard masonry coursing: two bricks placed with one mortar joint should align to neat multiples of 10 cm in nominal dimensions, confirming 20 × 10 × 10 cm nominal and 19 × 9 × 9 cm actual.

Why Other Options Are Wrong:

• 23 × 11.5 × 7.5 cm, 25 × 13 × 7.5 cm: Not standard modular sizes in Indian practice.
• 20 × 10 × 10 cm: This is the nominal size (includes mortar), not the actual unit size.
• None of these: Incorrect because 19 × 9 × 9 cm is correct.

Common Pitfalls:
Confusing nominal size with actual size; assuming the same dimensions are used globally; ignoring the mortar joint allowance in nominal dimensions.

Final Answer:
19 cm x 9 cm x 9 cm