DRAG DROP
You have an Office 365 tenant that uses an Enterprise E3 subscription.
You must prevent five specific users from using Skype for Business Online to send instant messages
to external users. All other users must be able to send instant messages to both internal and
external users.
You need to configure the environment.
Which three actions should you perform in sequence? To answer, move the appropriate actions
from the list of actions to the answer area and arrange them in the correct order.
Answer: 
Explanation:
To configure external communications for individual users
Open the Skype for Business admin center: Sign in to the Microsoft Online Services portal, and then
click Admin > Skype for Business.
Click Users, select the users whose settings you want to modify, and then click Edit
Click External communications, and then select or clear the options as appropriate:
* Skype for Business users Skype for Business users in federated domains
* People on public IM networks Users of the Skype public IM service.
Click Save.Review and configure Skype for Business settings
https://technet.microsoft.com/en-us/library/dn771172.aspx
There are no specific user options under “Organization”
Correct answer:
1. Navigate to the Skype for Business Admin Center and select the Users page
2. Select the user accounts that you need to configure
3. Select external communications and clear the public IM networks and Skype For Business users check boxes.
Agree with Kon, tried on my tenant and there aren’t any user options under “Organization”
In organization are global settings for external communications. In Users are settings for specific user.
Just a note, user settings are Skype for Business and Skype, not Skype for Business and Public IM networks.
But agree with Kon.
I agree under Organisation you disable/enable the external communication organisation wide not per-user. To disable for selected users, you have to edit the selected users’ configuration and disable the external communication.
I agree, you would definitely select User > External Communications (not Organization).
But the options appear to have been updated in 365, on this page I’m now seeing
“Choose people outside your organization that the user can communicate with,
O External Skype for Business users
O External Skype users”
So I guess the answer now is untick those boxes for those 5 users.
Agree with Kon