Helvetica vs. Arial
The letters which distinguish Helvetica from Arial (in this quiz) are: G, r, F, t, a, S, R, c and M. By looking only at these letters you can spot the helvetica. The differences are subtle but once you notice them it is easy to distinguish in a flash. Here a helpful chart from Ragbag:
Helvetica was developed in 1957 by Max Miedinger with Eduard Hoffmann at the Haas’sche Schriftgiesserei (Haas type foundry) of Münchenstein, Switzerland. Haas set out to design a new sans-serif typeface that could compete with Akzidenz-Grotesk in the Swiss market. Originally called Die Neue Haas Grotesk, it was created based on Schelter-Grotesk. The aim of the new design was to create a neutral typeface that had great clarity, had no intrinsic meaning in its form, and could be used on a wide variety of signage.
A contemporary sans serif design, Arial contains more humanist characteristics than many of its predecessors and as such is more in tune with the mood of the last decades of the twentieth century. The overall treatment of the curves is softer and fuller than in most industrial-style sans serif faces. Terminal strokes are cut on the diagonal which helps to give the face a less mechanical appearance.