$Mg^{2+}$ is isoelectronic with

If the atomic weight of an element is $23$ times that of the lightest element and it has $11$ protons,then it contains

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?

The atomic number of bromine is $35$ and its atomic weight is $79$. Two isotopes of bromine are present in equal amounts. Which of the following statements represents the correct number of neutrons?

Which number is common in isotopes?

Which character is different for the two isotopes of an element?