Option 1 states that both the assertion (A) and the reason (R) are true, and that R is the correct explanation of A.

Let`s analyze each statement separately:

- Assertion (A): The deficiency of Vitamin D causes rickets.

This statement is true. Rickets is a bone disease that occurs due to a lack of Vitamin D, which is essential for the absorption of calcium and phosphate in the body.

- Reason (R): The deficiency of Vitamin D leads to the increased loss of Ca++ in urine.

This statement is also true. When there is a deficiency of Vitamin D, the body is not able to properly absorb calcium from the diet, leading to a decrease in calcium levels. To maintain normal calcium levels, the body tries to get rid of excess calcium through the urine.

The reason (R) provided in option 1 correctly explains why the deficiency of Vitamin D causes rickets. Without adequate Vitamin D, the body loses calcium through urine, which disrupts calcium metabolism and bone development, resulting in rickets.

Therefore, option 1 is the correct answer as it states that both A and R are true, and R is the correct explanation of A.