It is really very important to know where the safety equipments are placed in lab because when we know it then accident wont occur in lab . it will also helps us to feel secure while doing any kinds of experiment
The best answer would be answer B. "the atom has a cloud of positive charge....."
Element X is sodium.
If there is one more shell of electrons, then this means it is one period below.
Since there is one less valence electron, it is one group to the left.