On the latest Android and iPad app I can mute/unmute at least a single room by tapping on the loudspeaker icon on the left side of the volume bar on the now playing screen/component. 

I think the guide could mention that slightly clearer:
https://www.sonos.com/en-us/guides/sonosapp

Thanks for the reply and link tip.  I can also Mute/unmute on ipad and android using the left loudspeaker icon of the volume bar but the problem is it Mutes all speakers in all rooms.  I just want to mute one speaker/room.  In addition, when I unmute using the left loudspeaker icon all of my speakers/rooms are unmuted including the speakers/rooms which were already muted prior to pressing the left loudspeaker icon.  I need to be able to Mute/unmute just one speaker/room like we could in the old app.  I run many sonos speakers throughout the house streaming the same station.  Most of the time some are Unmuted and some are Muted.  I need to be able to Mute/Unmute just one speaker/room at a time.  Do you know how I can do that?  It was available in the prior app.   Thanks.  

In addition, I need to be able to adjust the Volume of a single speaker/room using the sliders while that room is muted.  In the new app when you slide the volume slider while the speaker/room is Muted it is automatically Unmuted.  This can be quite disruptive when the volume is on high and you don’t want to wake everyone up with a blaring speaker that you are trying to turn down before unmuting.  In the prior app you could change the volume without Unmuting.  I need that feature back.  Thanks.

Ok, now I see what you mean. That feature seems to be still missing.

Indeed the only way to “mute” when speakers are grouped for me is to slide the volume slider to 0 for a single room in that “group UI” (the speaker-like icon on now playing screen). But obviously it is like you say that it will then unmute if I adjust the volume slider. 
 

There is that big speaker icon on that UI so hopefully it is a placeholder for the radio button and they’ll have that mute feature on their roadmap…

Touch the Group, then the Group Volume slide.