Close a single tab: Tap the Open tabs icon then tap the X in the upper-right corner of the tab that you want to close. You can also swipe the tab to the left or right off of the screen to close it.
Close Incognito tabs: Tap the Open tabs icon . From the stacked Incognito tabs view, tap the Menu icon (at the upper-right corner of the screen), then tap Close incognito tabs.
Close all tabs: Tap the Open tabs icon , tap the Menu icon (at the upper-right corner of the screen), then tap Close all tabs.
Closing the Chrome app (or even turning the phone off) will not close your open tabs. Your tabs remain open until you close them.