In Dobereiner's Triads, elements were written as:

Correct option is C

​The correct answer is (c) down the group with increasing atomic masses.

Explanation:

Dobereiner's Triads were an early attempt to classify elements based on their properties and atomic masses. Johann Wolfgang Döbereiner grouped elements into sets of three called triads, where:

1. Elements were arranged in groups of three (triads), based on their similar chemical properties.
2. The atomic mass of the middle element was approximately the average of the atomic masses of the other two elements in the triad.

Key Observations:

• The elements in a triad were arranged down the group with increasing atomic masses.
• Example of a Dobereiner's Triad:
• Lithium (Li), Sodium (Na), and Potassium (K)
• Atomic Mass of Li = 7
• Atomic Mass of Na = 23
• Atomic Mass of K = 39
• Na's atomic mass (23) is roughly the average of Li (7) and K (39): 

Average= $$\frac{7 +39}{2}$$  =   23​

Why Other Options Are Incorrect:

• Moving from left to right with increasing atomic masses: Dobereiner's Triads focused on grouping elements vertically (down the group), not horizontally.
• Down the group with decreasing atomic masses: Elements in Dobereiner's Triads are arranged with increasing atomic masses, not decreasing.
• Moving from left to right with decreasing atomic masses: This contradicts both the arrangement and concept of Dobereiner's Triads, as they do not involve decreasing masses or horizontal movement.

Information Booster:

• Limitation of Dobereiner’s Triads: It could only classify a few elements and was not applicable to all elements known at that time.
• Importance: It laid the groundwork for later classifications, such as the work of Mendeleev and the modern periodic table.