An atom having atomic mass number $13$ has $7$ neutrons. What is the atomic number of the atom?

The two stable isotopes of carbon present in naturally occurring carbon are

Which of the following pairs are isoelectronic with one another?

What is the atomic number and the number of electrons in a hydrogen atom (containing $1$ proton) and a sodium atom (containing $11$ protons) respectively?

Write the complete symbol for the atom with the given atomic number $(Z)$ and atomic mass $(A)$:
$(i)$ $\quad Z=17, A=35$
$(ii)$ $\quad Z=92, A=233$
$(iii)$ $\quad Z=4, A=9$

If the mass attributed to a neutron were halved and that attributed to the electron were doubled,the atomic mass of $_6C^{12}$ would