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.

Explanation

### Step-by-Step Text Solution

**Step 1: Identify the Physical Properties Used by Mendeleev**
Mendeleev arranged the elements in his periodic table primarily based on their atomic masses. This was a key physical property that he considered. He believed that the properties of elements were related to their atomic mass, and thus, he organized them in increasing order of atomic mass.

**Step 2: Identify the Chemical Properties Used by Mendeleev**
In addition to atomic mass, Mendeleev also took into account the chemical properties of elements. He specifically looked at how elements reacted with oxygen and hydrogen, which are fundamental elements in many chemical reactions. This helped him group elements with similar chemical behaviors together.

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