Writing a sentence that is true in one model and false in the other

Question

Let $Σ=(R)$, where $R$ is a binary relation. Write a sentence that is true in $\mathcal M_1$ but false in $\mathcal M_2$:

$$\mathcal M_1=(P(N),⊂)$$

$$\mathcal M_2=(N,<)$$

I've been trying to find this sentence for a couple of hours now and they just seem too equivalent, every sentence that i find is either good for both of them or bad for both of them,

Thanks in advance !

Answer 1

HINT: There is nothing in $M_2$ corresponding to the relationship between the subsets $\{1\}$ and $\{2\}$ of $\Bbb N$ in $M_1$. Your sentence should start $\exists x\,\exists y\ldots$.