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Q.5
                       Assertion: If the pH inside the mouth decreases below 5.5, the decay of
                       tooth enamel begins.
                       Reason:  The bacteria present in mouth  degrades the  sugar  and left
                       over food particles and produce acids that remains in the mouth after
                       eating.



               SUBJECTIVE QUESTIONS:

                 S.L                                 Questions                                 Mark  Skill
                 No.
                 Q.1                                                                           1       R
                        At what pH in the mouth is tooth decay faster and   why?


                        [CBSE 2008]
                 Q.2                                                                           1       u
                        What measures you will take when a person gets bitten
                        by honeybee.
                 Q.3                                                                           3       R+A
                        The pH of the mouth of a person is lower  than 5.5.
                        What changes will occur in his mouth? How these
                        changes can be controlled? Write any two measures.

                           [CBSE 2012, 2011, 2010]

                 Q.4    pH has a great importance in our daily life. Explain                   3       U+A
                           by giving three examples.             [CBSE Sample
                           Paper 2018]

                 Q.5                                                                           5       HOT
                        (a) Mention the Ph range within which our body works.
                        Explain how antacids give relief from acidity.  Write the
                        name of one such antacid.

                        (b) Fresh milk has a Ph of 6.   How does the Ph will
                        change as it turns to curd? Explain your answer.
                         (c) A milkman add a very small amount of baking soda
                        to fresh milk.  Why does this milk take a longer time to
                        set as curd?

                        (d) Mention the nature of tooth pastes.  How do they
                        prevent tooth decay?












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