Let the price of mangoes be \( x \) rupees per kg and the price of oranges be \( y \) rupees per dozen.
From Statement I:
Ten kg of mangoes and two dozen oranges cost Rs. 252. So we get:
\[
10x + 2y = 252 \tag{1}
\]
This is a linear equation in two variables \( x \) and \( y \), so we cannot determine the value of \( x \) alone.
From Statement II:
Two kg of mangoes = one dozen oranges, in terms of value. That means:
\[
2x = y \tag{2}
\]
This gives a relationship between \( x \) and \( y \), but not the value of either.
Using both statements I and II:
From (2), substitute \( y = 2x \) into equation (1):
\[
10x + 2(2x) = 252 10x + 4x = 252 14x = 252 x = 18
\]
So, the price of mangoes per kg is \( \boxed{18 \text{ rupees}} \)