Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic Table?

In Mendeleev's Periodic Table, gaps were left for the elements to be discovered later. Which of the following elements found a place in the periodic table later

Which of the following statements about the Modern Periodic Table is correct:

An element which is an essential constituent of all organic compounds belong to 

Which of the following gives the correct increasing order of the atomic radii of O, F and N?

Which of the following elements does not lose an electron easily?

Arrange the following elements in the order of their increasing nonmetallic character : Li, O, C, Be, F

On moving from left to right in a period in the periodic table, the size of the atom.

Lithium, sodium and potassium form a Dobereiner's triad. The atomic masses of lithium and potassium are 7 and 39 respectively. Predict the atomic mass of sodium.

How many vertical columns are there in the modern periodic table and what are they called?

What were the limitations of Newlands' Law of Octaves?

What were the criteria used by Mendeleev in creating his Periodic Table?

How could the Modern Periodic Table remove various anomalies of Mendeleev's Periodic Table?

(a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?
(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

(a) What property do all elements in the same column of the Periodic Table as boron have in common?
(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?

Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?

Write the number of periods the modern periodic table has. How do the valency and metallic character of elements vary on moving from left to right in a period? How do the valency and atomic size of elements vary down a group?

What physical and chemical properties of elements were used by Mendeleev in creating his periodic table? List two observations which posed a challenge to Mendeleev's Periodic Law.

Table given below shows a part of the Periodic Table.

Using this table explain why?
(a) Li and Na are considered as active metals.
(b) Atomic size of Mg is less than that of Na.
(c) Fluorine is more reactive than Chlorine.

Atomic number of a few elements are given below 10, 20, 7, 14
(a) Identify the elements.
(b) Identify the Group number of these elements in the Periodic Table.
(c) Identify the Periods of these elements in the Periodic Table.
(d) What would be the electronic configuration for each of these elements?
(e) Determine the valency of these elements.

An element A which is a yellow solid at room temperature shows catenation and allotropy. A forms two oxides which are also formed during the thermal decomposition of ferrous sulphate crystals and are the major air pollutants.
(a) Identify the element A
(b) Write the electronic configuration of A
(c) Write the balanced chemical equation for the thermal decomposition of ferrous sulphate crystals?
(d) What would be the nature (acidic/ basic ) of oxides formed?
(e) Locate the Position of the element in the Modern Periodic Table.

Which group of elements could be placed in Mendeleev's Periodic Table without disturbing the original order? Give reason

Give an account of the process adopted by Mendeleev for the classification of elements. How did he arrive at "Periodic Law"?

Explain the trends in the modern Periodic Table of various properties like valency, atomic size, metallic and non-metalic properties of the atoms of elements.

(a) Why do we classify elements?
(b) What were the two criteria used by Mendeleev in creating his Periodic Table?
(c) Why did Mendeleev leave some gaps in his Periodic Table?
(d) In Mendeleev's Periodic Table, why was there no mention of Noble gases like Helium, Neon and Argon?
(e) Would you place the two isotopes of chlorine, Cl-35 and Cl-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.