Of the known elements in the periodic table, only ______ are gases under normal atmospheric conditions.

11

The correct answer is option (1) 11.

There are 11 elements that exist as gases under normal atmospheric conditions (temperature around 25°C and pressure around 1 atm). These elements belong to two categories:

Noble gases (Group 18):  Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn).

Other non-metals:  Hydrogen (H), Nitrogen (N), Oxygen (O), Fluorine (F), and Chlorine (Cl).

Therefore, out of the given options, 11 is the accurate number of elements that are gases under normal atmospheric conditions.