Explanation:

- To find the smallest positive number to subtract from 2 and 3 so that 4 becomes the third proportion, let's denote the number as 'x'.

- The concept of third proportion implies that if a, b, and c are in proportion (a:b = b:c), then b^2 = a * c.

- Here, subtract x from both 2 and 3: (2-x):(3-x) should equal (3-x):4.

- So, the equation becomes (3-x)^2 = (2-x) * 4.

- Solving, you get: 9 - 6x + x^2 = 8 - 4x.

- Simplifies to x^2 - 2x + 1 = 0.

- This factors to (x-1)^2 = 0, giving x = 1.

- Answer: Option 1: 1