You surely have an experience of asking "Are you ok ?" to whole of students.
Is your asking of "Are you ok ?" working ?
Does some student answer "No" ?
"Are you ok ?" works only if you are successful in training your students so that they do not think it shameful to say "No, I have no idea."
There are techniques to know how each student is.
Here is a technique :
After you made an instruction, let all students stand up. And say : "If you understand it, sit down."
If there remains students who are standing, make an instruction. And say "If you understand now, sit down."
Repeat 2.
But this works on the following condition :
Students do not think that being unable to understand is a shame.
It is your important business to satisfy this condition.