The correct answer is: Only 1.
Saach Pass connects Chamba valley with Pangi valley. This is a correct statement. Saach Pass is a high mountain pass in the Pir Panjal Range of the Himalayas. It is located in the Chamba district of Himachal Pradesh, India. The pass is at an elevation of 4,420 meters (14,500 feet). It connects the Chamba valley with the Pangi valley.
Kiarda Dun valley in Sirmaur is separated from Dehradun valley by Yamuna river. This is an incorrect statement. Kiarda Dun valley is located in the Sirmaur district of Himachal Pradesh, India. The valley is separated from the Dehradun valley by the Yamuna river. However, the Yamuna river does not flow through the Kiarda Dun valley.
Therefore, only statement 1 is correct.