Answer:
The 3rd one is correct
Explanation:
Protons and neutrons have approximately the same mass, about 1.67 × 10−24 grams, which scientists define as one atomic mass unit (amu) or one Dalton. Each electron has a negative charge (−1) equal to the positive charge of a proton (+1). Neutrons are uncharged particles found within the nucleus.
A because a primary source is defined as a first hand account of an event .
I think it’s C but I’m not sure
Answer: Elements in the last period are radioactive.
Explanation: