In this question, we are given the heights of five friends - Sachin, Kunal, Mohit, Amit, and Sohan. To determine who will be the third in the order of increasing heights, we need to analyze the given information.

1. Sachin is shorter than Kunal but taller than Sohan: From this information, we can conclude that the order of heights from shortest to tallest will be Sohan, Sachin, Kunal.

2. Mohit is the tallest: This indicates that Mohit will be the last in the order of increasing heights.

3. Amit is little shorter than Kunal and little taller than Sachin: This suggests that Amit will be between Kunal and Sachin in terms of height.

Based on the above analysis, we can conclude that Amit will be the third in the order of increasing heights.

Therefore, the correct answer is option 1 - Amit.