Option 1 states that both the assertion (A) and reason (R) in the question are true, and that the reason is the correct explanation of the assertion. Let`s analyze each part separately:

Assertion (A): Deficiency of Vitamin D causes rickets in children.

Explanation: This statement is true. Rickets is a bone disorder that primarily affects children and is characterized by soft, weak bones. Vitamin D deficiency is a known cause of rickets because it plays a key role in promoting the absorption of calcium and phosphorus, which are essential for bone mineralization. Without enough vitamin D, the body is unable to properly absorb and use these minerals, leading to the development of rickets.

Reason (R): Deficiency of Vitamin D causes increased loss of Ca++ in urine.

Explanation: This statement is also true. Vitamin D deficiency can lead to increased loss of calcium in the urine. Without enough vitamin D, the intestines do not absorb enough calcium from the diet, leading to low blood calcium levels. To compensate for this, the body increases the excretion of calcium in the urine, resulting in a net loss of calcium from the body.

Therefore, option 1 is correct because both the assertion and reason are true, and the reason provides a valid explanation