Option 4 is correct, i.e. Francium.

Among the given elements Francium is the highest atomic number which is 87.

Extra facts:

Henry Moseley classified elements based on Atomic numbers.

In 1913 A.D. the English scientist Henry Moseley demonstrated, with the help of the experiments done using an X-ray tube, that the atomic number (Z) of an element corresponds to the positive charge on the nucleus or the number of protons in the nucleus of the atom of that element.

This revealed that ‘atomic number’ is a more fundamental property of an element than its atomic mass.

The general valency of electropositive elements is 1, 2, 3.

Atoms which tend to donate electrons and converts into a positive ion (M+) are called Electropositive atoms.

The atoms which have 1, 2, or 3 electrons in their valence shells will lose their electrons to attain a stable electronic configuration.

Some examples are Sodium, Magnesium, and Aluminium. These 3 elements will lose electrons to attain the configuration of the noble gas Neon. 

Lithium (Li) element has the largest atom.

Largest atom is defined by its atomic radius i.e. the distance between nucleus to its outermost orbit/ valency shell.

As we move from left to right in the periodic table the atomic radius decreases.

But as we go down the period in the periodic table the atomic radius increases.

Hence lithium has the largest atom and it is greater than Hydrogen (H), Oxygen (O) and Fluorine(F).

Key Points

When quick lime (CaO)reacts with water, lime water is produced.

CaO +H₂O→Ca(OH)₂

Here the product is Ca(OH)₂, which is slaked lime or lime water.

Mainly Calcium carbonate disassociates to produce quick lime and carbon dioxide.

Then the quick lime reacts with water and produces lime water.

Calcium hydroxide is used in many applications, including food preparation.

Limewater is the common name for a saturated solution of calcium hydroxide.

Atomic number 56, Barium belongs to s - block elements.

Electronic configuration for the Barium [Xe]6s²

Modern Periodic Table is classified into the following elements - p-block, s-block, d-block, and f-block.

s-block elements include alkali metals and alkaline earth metals.

The word ‘atom’ is coined by Democritus.

He suggested that if we go on dividing matter at a certain point the atom becomes indivisible or cannot be divided further.

He called these particles as atoms (Indivisible).

Key Points

Element A has 18 protons.

The number of protons in an atom is also known as its atomic number and it determines the identity of the atom.

In an electrically neutral atom, the number of protons is equal to the number of electrons. So, in an atom of element A, which is neutral, there are also 18 electrons.

The symbol A+ denotes an ion of element A. An ion is an atom or group of atoms that have gained or lost one or more electrons, giving it a net positive or negative charge.

The "+" sign denotes that the atom has lost an electron.

It is positive because the number of positively charged protons now exceeds the number of negatively charged electrons.

Therefore, the A+ ion will have one fewer electron than a neutral A atom. Given that the neutral A atom has 18 electrons, the A+ ion will have 17 electrons

The Effective Atomic Number (EAN) of [A(NH₃)₆]Cl₃ is 33.

Each ammonia molecule contributes two electrons.

The contribution from six ammonia molecules is 6 × 2 = 12.

The oxidation state of the metal is +3.

Let the atomic number of the metal be 'x'.

The total number of electrons from the unit [A(NH₃)₆]³⁺ is:

x + 12 -3 = 33

or, x = 24.

Hence, the atomic number of the element is 24.

Isobars: The nuclei which have the same mass number (A) but a different atomic number (Z) are called isobars.

Examples of Isobars are ¹⁴ C ₆, ¹⁴ N ₇

Property of isobars:

The atomic masses are equal

Often the physical properties are similar

Atomic numbers are different

Chemical elements are different

Chemical properties also different.

Hence we can conclude that Isobars have sane mass number.