Let's solve this problem step by step:

Given:
- Mohan pays a total of 35 coins in 1 rupee and 2 rupee coins.
- The ratio of 1 rupee coins to 2 rupee coins is 2:5.

Step 1: Calculate the number of 1 rupee coins and 2 rupee coins.
Let the number of 1 rupee coins be 2x.
Then the number of 2 rupee coins will be 5x.

Step 2: Calculate the total amount of money paid by Mohan.
The value of each 1 rupee coin is 1 rupee.
The value of each 2 rupee coin is 2 rupees.
So, the total amount paid by Mohan can be calculated as:
Total amount = (number of 1 rupee coins * value of 1 rupee) + (number of 2 rupee coins * value of 2 rupees)
Total amount = (2x * 1) + (5x * 2)
Total amount = 2x + 10x
Total amount = 12x

Step 3: Calculate the total amount paid by Mohan in terms of coins.
The total number of coins paid by Mohan is given as 35.
So, 12x = 35
Dividing both sides of the equation by 12, we get:
x = 35/12
x = 2.92

Since the number of coins cannot be in decimal, we round down the value of x to the nearest whole number.
So, x = 2.

Step 4: Calculate the number of 1 rupee coins and 2 rupee coins.
Number of 1 rupee coins = 2x = 2 * 2 = 4
Number of 2 rupee coins = 5x = 5 * 2 = 10

Step 5: Calculate the total value of coins paid with the mistake.
The value of each 5 rupee coin is 5 rupees.
So, the total value of coins paid with the mistake can be calculated as:
Total value = (number of 1 rupee coins * value of 1 rupee) + (number of 5 rupee coins * value of 5 rupees)
Total value = (4 * 1) + (10 * 5)
Total value = 4 + 50
Total value = 54

Step 6: Calculate the amount paid with the mistake in terms of coins.
The total number of coins paid with the mistake is given as 35.
So, 54 = 35 + (number of 5 rupee coins)
Number of 5 rupee coins = 54 - 35
Number of 5 rupee coins = 19

Step 7: Calculate the number of 5 rupee coins Mohan should receive back from the shopkeeper.
Since Mohan gave the shopkeeper 5 rupee coins instead of 2 rupee coins, the shopkeeper should return the difference.
Number of 5 rupee coins to be returned = Number of 5 rupee coins - Number of 2 rupee coins
Number of 5 rupee coins to be returned = 19 - 10
Number of 5 rupee coins to be returned = 9

Therefore, Mohan should receive back 9 five