のも当然だ・わけだ: the difference
のも当然だN2
Meaning
It is only natural that, It is no wonder
Past papers
Example
税金を納めていないんだから、逮捕されるのも当然です。
Since (he) didn't pay (his) taxes, it is only natural that (he) would be arrested.
わけだN3
Meaning
For that reason, No wonder, As you'd expect, Naturally, Thus, This is why
Past papers
Tested 6 times in past papers
Example
雪が降っていた。寒い訳だ。
It snowed, so as you'd expect, it's cold.
How to tell them apart
「〜のも当然だ」: you judge that this is only reasonable.
「〜わけだ」: a sudden 'now I see, no wonder': 「暑いわけだ、38度もある」 (No wonder it's hot, it's 38 degrees).
Forms: na-adjective + 「な」; noun + 「も当然だ」, as in 「それも当然だ」.