Aman was discussing the structure of atom with his classmates. During the discussion, he learnt that an element X has a mass number of 35 and contains 18 neutrons. Based on this information, answer the given questions:

(A) How many electrons and protons does element X have?

(B) What is its atomic number?

(C) Identify the element X.

(D) Write its electronic configuration.

(E) How many valence electrons does it have?

(F) What will be the mass number if two neutrons are added to its nucleus?

(G) What will be the relation of X with the new atom?

(A) Number of protons = Mass number (A) - Number of neutrons

= 35 - 18 = 17

Since the atom is electrically neutral, the number of electrons is equal to the number of protons. Therefore, the number of electrons = 17.

(B) Atomic number (Z) = Number of protons = 17

(C) The element with atomic number 17 is chlorine (Cl).

(D) Distributing 17 electrons in the shells (K, L, M) using the $2n^2$ rule:

K = 2, L = 8, M = 7. Therefore, electronic configuration is 2, 8, 7.

(E) The valence shell is the outermost shell, which is the M-shell containing 7 valence electrons.

(F) Original element X has:

Number of protons = 17

Number of neutrons = 18

If two neutrons are added:

New number of neutrons = 18 + 2 = 20

Mass number = Number of protons

+ Number of neutrons

= 17 + 20 = 37

So, the new mass number will be 37.

(G) The new atom has the same atomic number (17) as X but a different mass number (37 instead of 35). Atoms of the same element having the same atomic number but different mass numbers are called isotopes. Therefore, X and the new atom are isotopes of each other ($^{35}$Cl and $^{37}$Cl).