When atoms are joined together, they form A. protons
B. electrons
C. molecules
D. nuclei

hi

Explanation:

protons,electrons and neutrons form atoms and

atoms form molecules

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molecules

Explanation:

When atoms are joined together, they form molecules.

The nuclei is the centre part of an atom which contains proto s in it and electrons are the negatively charged sub-atomic particles which is present outside the nuclei. These are located inside the atoms but molecules are the smallest particle of an element or compound. They are formed my combining atoms together.

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.