What is the direction of this acceleration?
The acceleration is parallel to $\vec{v}$ and perpendicular to $\vec{B}$ and so is vertical, along the particle's path
The acceleration is perpendicular to $\vec{v}$ and parallel to $\vec{B}$ and so is horizontal, along the particle's path.
The acceleration is perpendicular to $\vec{v}$ and $\vec{B}$ and so is horizontal, toward the center of curvature of the particle's path
The acceleration is perpendicular to $\vec{v}$ and $\vec{B}$ and so is horizontal, out of the center of curvature of the particle's path