Rigid PVC (unplasticized, uPVC) is hard, strong, and resistant to chemicals and weathering, making it ideal for pipes, window frames, and fittings. Flexible PVC uses plasticizers. It is not biodegradable. Transparency depends on additives; generally it's translucent. Its chemical resistance is due to the chlorine content.
Explanation:
J.J. Thomson discovered the electron in 1897 using cathode ray tubes and determined its e/m ratio. Rutherford discovered the nucleus; Chadwick discovered neutron; Bohr proposed quantized model.
Consider the following statements about the modern periodic table: 1. Elements are arranged by atomic mass. 2. It has 18 groups and 7 periods. 3. The f-block elements are called inner transition metals. Which are correct?
Explanation:
The modern periodic table is based on atomic number, not atomic mass (Mendeleev's table was based on mass). It consists of 18 vertical groups and 7 horizontal periods. The f-block elements, placed at the bottom, are indeed called inner transition metals (lanthanides and actinides). Thus, statements 2 and 3 are correct.
Explanation:
Sodium reacts vigorously with moisture and oxygen in air, so it is stored under kerosene to prevent contact. Potassium, lithium are similarly stored. Iron, zinc, copper do not require such storage.
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