An object moving in the $+x$ axis experiences an acceleration of $2\mathrm{.}0\frac{m}{s^2}.$ This means the object is

changing its velocity by $2\mathrm{.}0\frac{m}{s}.$

traveling at $2\mathrm{.}0$ m in every second.

traveling at $2\mathrm{.}0\frac{m}{s}$ in every second.

increasing its velocity by $2\mathrm{.}0\frac{m}{s}$ in every second.