Many things in the arithmetic of abelian varieties have counterparts not only in linear tori, but also for semisimple linear groups. Two examples are the Tamagawa number and the conjectured finiteness of the Shafarevich-Tate group.

I wanted to ask about the Mordell conjecture (proved by Faltings and Vojta), which for a complex semiabelian variety $A$ and a finitely generated subgroup $\Gamma \subset A(\mathbb{C})$ states that the Zariski closure of any subset of $\Gamma$ is the union of finitely many cosets of algebraic subgroups of $A$.

For $\mathrm{SL}_2$ the obvious translation of this statement is false: the arithmetic subgroup $\mathrm{SL}_2(\mathbb{Z})$ is generated by two elements and contains a Zariski-dense subset from the algebraic set $\mathrm{tr}(A) = 0$. (One could still ask if there is any description of the possible Zariski closures $V$ of subsets of arbitrary finitely generated subgroups $\Gamma \subset G(\mathbb{C})$ of the complex points of a linear group $G$. Taking cue from this example I had asked whether, for instance, such a $V$ has to be defined over a number field. As Venkataramana explains in his answer below, this question is meaningless as it stands: at the very least, I must remove from $V$ a finite union of algebraic subgroup cosets, thereby focusing on the counterexamples to the literal Mordell-type statement.)

Perhaps the analogs of the Manin-Mumford and Bogomolov problems (which concern the Zariski closures of sets of points of finite order) could make more sense in linear groups. Instead of attempting to make any more hasty guesses of how the structure of the possible Zariski closures might look like, it would be more prudent to just record this as an open-ended problem:

**Problem.** 1. *Describe the possible Zariski closures $V$ of sets of elements of finite order in $G(\mathbb{C})$.* 2. *Whatever these $V$ are, do they coincide with the set of subvarieties of $G$ which possess a Zariski-dense sequence of semisimple elements of $G(\bar{\mathbb{Q}})$ all of whose eigenvalues have canonical Weil heights approaching zero?*