A teacher asked to give and example for Dobereiner's tried . Ramu Wrote then as `'' Li ,Na ,Mg'' ` . In these , identify which element does not belongs to this tried ?

Which of the following is not an example of Dobereiner's Traids a) Ca, Sr. Ba b) Cl, Br, I c) Li, Na, K d) Sr, Ba, Ra

The elements of a period of the periodic table are given below in order from left to right with one of its element missing: Na Mg Al Si S Cl Ar . (a) To which period do these elements belong? (b) One element of this period is missing. Which is the missing element and where should it be placed? (c) Which one of these elements in this period shows the property of catenation? (d) Which one of these elements is least reactive? (e) Identify the halogen from this period.

Read the passage given below and answer the following questions: Although actinoids are similar to lanthanoids in that their electrons fill the 5f orbitals in order, their chemical properties are not uniform and each element has characteristic properties. Promotion of 5 - 6d electrons does not require a large amount of energy and examples of compounds with 77 acid ligands are known in which all the 5f, 60, 7s, and 7p orbitals participate in bonding. Trivalent compounds are the most common, but other oxidation states are not uncommon. Especially, thorium, protactinium, uranium, and neptunium tend to assume the +4 or higher oxidation state. There are 14 elements in actinoid series. Which of the following element does not belong to this series?