I know this sounds silly. However am not getting any article / post which explicitly says that 'SharePoint Online will open MS Office documents (word, excel, ppt) in Browser (Office Online)'.
Moreover looking at the Compare SharePoint Online options getting an impression that 'SharePoint Online Option 1' which doesn't include 'Office Applications' will download Office files to client computer.
Kindly confirm "Whether SharePoint Online will open's Office documents like word excel etc in Office Online i.e. in Browser or not?"