National Science Olympiad Model Paper 3 Questions and Answers Part 29

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29. Which of the following statements about Rutherford՚s model of atom are correct?

(A) Considered the nucleus as positively charged

(B) Established that the α – particles are four times as heavy as a hydrogen atom

(C) Can be compared to the solar system

(D) Was in agreement with Thomson՚s model

Choose the Correct Option

(a) (A) and (C)

(b) (B) and (C)

(c) (A) and (D)

(d) Only (A)

Answer: a

Explanation:

The positively charged particles and most of the mass of an atom was concentrated in an extremely small volume. He called this region of the atom as a nucleus.

Rutherford model proposed that the negatively charged electrons surround the nucleus of an atom. He also claimed that the electrons surrounding the nucleus revolve around it with very high speed in circular paths. He named these circular paths as orbits.

Electrons being negatively charged and nucleus being a densely concentrated mass of positively charged particles are held together by a strong electrostatic force of attraction

30. Number of molecules in 100 ml of each of O2, NH3 andCO2at STP are

A) In the order CO2 < O2 < NH3

B) In the order NH3 < O2 < CO2

C) Will be same

D) NH3 = CO2 < O2

Answer: C

Explanation:

According to Avogadro՚s hypothesis equal volumes of all gases under similar conditions of temperature and pressure contains equal no. of molecules.

Avogadro explained that the volumes of all gases can be easily determined.

Statement: For equal volumes of all gases at the same temperature and pressure contain equal numbers of particles. Since the total volume that a gas occupies is made up primarily of the empty space between the particles, the actual size of the particles themselves is nearly negligible.

Standard temperature and pressure (STP) is defined as 0 (273.15K) and 1atm pressure. The molar volume of a gas is the volume of one mole of a gas at STP. At STP, one mole representative particles of any gas occupies a volume of 22.4L

31. Which of the following element supports the Bohr՚s model.

Illustration: National Science Olympiad Model Paper 3 Questions and Answers Part 29

A) Boron

B) Magnesium

C) Neon

D) Sodium

Answer: D

Explanation:

Sodium has atomic number 11, So it has number electron equal to11and needs 3 electron Shell. The Bohr Mosel represents the electrons by the 11 dots

First has capacity 2 electron

Second has capacity 8 electron

Third shell has capacity 18 and one electron left so outermost shell has one electron and it has ability to lose electron to form cation.

32. Read the statement identify the animal

Statement: A animals which is present in water mostly marine ecosystem as well as some in freshwater ecosystem form and show radial symmetry. The organism show two body form and layer are diploblastic.

I. Hydra

II. Sea anemones

III. Sponges

IV. Ascaris

Choose the Correct Option

A) Both I and II

B) Both I and III

C) Both III and V

D) Only IV

Answer: A

Explanation: Cnidarian, also called coelenterate, any member of the phylum Cnidaria (Coelenterate) , a group made up of more than 9,000 living species. Mostly marine animals, the cnidarians include the corals, hydras, jellyfish, Portuguese men-of-war, sea anemones, sea pens, sea whips, and sea fans

Characteristics

Radially Symmetrical.

Body multicellular, few tissues, some organelles.

Body contains an internal cavity and a mouth.

Two different forms exist, medusa and polyp.

Reproduction is asexual or sexual.

Has a simple net like nervous system.

Has a distinct larval stage which is planktonic.