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➡️What are some Unique Characteristics of pteridophytes ??
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Answers
Answer:
Question. 1. Name the scientist who laid the foundation of chemical sciences. How ?
Answer. Antoine Laurent Lavoisier, by establishing two important laws of chemical combination.
Question. 2. Define law of conservation of mass.
Answer. It states that, ‘Mass is neither created nor destroyed in a chemical reaction.’ In other-words, the mass of the reactants must be equal to the mass of products.
Question. 3. Define law of constant proportion.
Answer. It states that, ‘In a pure chemical substance, the elements are always present in definite proportions by mass’.
Question. 4. Which organisation approves the names of elements all over the world ? Write the symbol of gold. [SA II-2014]
Answer.
International Union of Pure and Applied Chemistry (IUPAG).
Au.
Question. 5. Write the symbols of tungsten and iron.
Answer. (i) Tungsten (W) (ii) Iron (Fe).
Question. 6. Name the element which is used as the reference for atomic mass.
Answer. Carbon.
Question. 7. ‘Atoms of most elements are not able to exist independently’. Name two atoms which exist as independent atoms. [SA II-2012]
Answer. Noble gases such as argon (Ar), helium (He) exist as independent atoms.
Question. 8. What is the number of electrons in Mg atom and { Mg }^{ 2+ } ion ? [SA II-2014]
Answer. Mg:{ 12 }^{ e- }:{ Mg }^{ 2+ }:{ 10 }^{ e- }
Question. 9. Which of the following species is electrically neutral and why ? [SA II-2014]
Answer. { Na }^{ + },{ Cl }^{ - }{ K }^{ + };Na,{ Ca }^{ +2 }
Question. 10. Write atomicity of the following:
(i) Sulphur, (ii) Phosphorus [SA 11-2014]
Answer. (i) Polyatomic, (ii) Tetra atomic.
Question. 11. Define atomicity.
Answer. The number of atoms present in one molecule of an element or a compound is known as its atomicity.
Question. 12. What are polyatomic ions ? Give two examples.
Answer. A group of atoms having a charge is known as polyatomic ion.
Examples : { NH }_{ 4 }^{ 1+ },{ SO }_{ 4 }^{ 2- }
Question. 13. What is the atomicity of Argon ?
Answer. Mono atomic.
Question. 14. Give one relevant reason why scientists choose 1/16 of the mass of an atom of naturally occurring oxygen as the atomic mass unit.
Answer. Initially 1/16th of the mass of naturally occurring oxygen was taken as the atomic mass unit because this unit gave masses of most of the elements as whole numbers.
Question. 15. State the number of hydrogen atoms in 1 g of hydrogen.
Answer. One gram of hydrogen = One mole
=6.022 x { 10 }^{ 23 } atoms
Question. 16. What is molar mass ? What are its units ?
Answer. The mass of one mole of a substance is called its molar mass. Its unit is gram per mole (g { mol }^{ -1 }).
Question. 17. Define atomic mass unit.
Answer. One atomic mass unit is a mass unit equal to exactly one twelfth (1/12th) the mass of one atom of carbon -12.
Question. 18. The relative atomic mass of oxygen atom is 16. Explain its meaning.
Answer. The relative atomic mass of an atom is the average mass of the atom, as compared to 1/12th the mass of one carbon-12 atom.
Question. 19. Distinguish between molecular mass and molar mass.
Answer. The molecular mass of a substance is the sum of the atomic masses of all atoms in a molecule, whereas the mass of 1 mole of any substance is called its molar mass.
Question. 20. Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass ? [SAII-2011]
Answer. Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction.
Question. 21.Which postulate of Dalton’s atomic theory can explain the law of definite proportions ? [SAII-2011]
Answer. Atoms combine in the ratio of small numbers to form compounds. In a compound, the relative number and kinds of atoms are constant.
Question. 22. Define the atomic mass unit. [SAII -2011]
Answer. The mass of 1/12 part of C-12 is equivalent to one atomic mass unit. Previous, it was denoted by symbol amu but now, these days it is denoted by symbol u.
Question. 23. Why is it not possible to see an atom with naked eyes ?
Answer. Because an atom is too small, i.e., the atomic radii of an atom is of the order { 10 }^{ -10 } m to { 10 }^{ -9 } m.
Question. 24. What is meant by the term chemical formula ?
Answer. The chemical formula of a compound is a symbolic representation of its composition and actual number of atoms in one molecule of a pure substance, may be an atom or a compound.
Question. 25. How many atoms are present in a (i) { H }_{ 2 }S molecule and (ii) { PO }_{ 4 }^{ 3- }ion ? [SAII – 2011]
Answer. (i) In { H }_{ 2 }S, 3 atoms are present (ii) In { PO }_{ 4 }^{ 3- }, 5 atoms are present.
Pteridophyta Characteristics
1. Pteridophytes are considered as the first plants to be evolved on land:
=>It is speculated that life began in the oceans, and through millions of years of evolution, life slowly adapted on to dry land. And among the first of the plants to truly live on land were the Pteridophytes.
2. They are cryptogams, seedless and vascular:
=>Pteridophytes are seedless, and they reproduce through spores. They contain vascular tissues but lack xylem vessels and phloem companion cells.
3. The plant body has true roots, stem and leaves:
=>They have well-differentiated plant body into root, stem and leaves.
4. Spores develop in sporangia:
=>The sporangium is the structures in which spores are formed. They are usually homosporous (meaning: one type of spore is produced) and are also heterosporous, (meaning: two kinds of spores are produced.)
5. Sporangia are produced in groups on sporophylls:
=>Leaves that bear the sporangia are termed as sporophylls. The tip of the leaves tends to curl inwards to protect the vulnerable growing parts.
6. Sex organs are multicellular:
=>The male sex organs are called antheridia, while the female sex organs are called archegonia.
7. They show true alternation of generations:
=>The sporophyte generation and the gametophyte generation are observed in Pteridophytes. The diploid sporophyte is the main plant body.