ANSWER -
No, we cannot assume that all Silicon atoms have 14 neutrons just based on its position in the periodic table. The atomic number of Silicon is 14, which means that the number of protons in the nucleus of a Silicon atom is 14. However, the number of neutrons in a Silicon atom can vary, as isotopes of Silicon exist with different numbers of neutrons.
The most common isotope of Silicon has 14 neutrons, but there are also isotopes with 15 or 13 neutrons. The relative abundance of each isotope depends on the source of the Silicon. For example, Silicon extracted from natural sources, such as rocks or sand, will have a different isotopic composition than Silicon produced synthetically. Therefore, we cannot make any assumptions about the number of neutrons in a Silicon atom without further information.