Explanation:

- Option 1: Rivalry

- Correctly spelt. Refers to competition or contention between parties.

- Option 2: Summary

- Correctly spelt. It means a brief statement or account of the main points of something.

- Option 3: Primary

- Correctly spelt. This word signifies something of chief importance or occurring first in a sequence.

- Option 4: Gallary

- Incorrectly spelt. The correct spelling is "Gallery," which refers to a room or building for displaying artworks.

Option: 4 - Gallary is the incorrectly spelt word. .