a nuke kills 10% of the army present on the op/colony it landed on

so that means if i launch 10 nukes and they arrive at the same tick does that kill 100% or it doesn't work that way?

They will hit one after another.

So if the target has 100 units the attack will go as follows:

Nuke 1 - 10 units - 90 units remain
Nuke 2 - 9 units - 81 units remain
Nuke 3 - 8 units - 73 units remain
Nuke 4 - 7 units - 66 units remain
Nuke 5 - 7 units - 59 units remain
Nuke 6 - 6 units - 53 units remain
Nuke 7 - 5 units - 48 units remain
Nuke 8 - 5 units - 43 units remain
Nuke 9 - 4 units - 39 units remain
Nuke 10 - 4 units - 35 units remain

So 10 nukes killed off 65% of the army on the outpost. Nukes are more effective if followed by ranged units (especially R4 and R5 units)

P.S. I dont know how the rounding goes so this may be slightly innaccurate.

-Pete