The correct answer is 6
Case I: When number is 4-digit number \((\overline{a\ b\ c\ d})\)
Here d is fixed and d=5
So, (a, b, c) can be (6, 4, 3), (3, 4, 6), (2, 3, 6), (6, 3, 2), (3, 2, 4) or (4, 2, 3)
⇒ 6 numbers
Case II: No number possible
Considering Bohr’s atomic model for hydrogen atom :
(A) the energy of H atom in ground state is same as energy of He+ ion in its first excited state.
(B) the energy of H atom in ground state is same as that for Li++ ion in its second excited state.
(C) the energy of H atom in its ground state is same as that of He+ ion for its ground state.
(D) the energy of He+ ion in its first excited state is same as that for Li++ ion in its ground state.


A slanted object AB is placed on one side of convex lens as shown in the diagram. The image is formed on the opposite side. Angle made by the image with principal axis is: 
Natural numbers are the set of positive integers (whole numbers greater than zero) that are used for counting and ordering. The set of natural numbers is denoted by the symbol N, and it includes all positive integers from 1 to infinity.
For example, the first few natural numbers are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and so on. Natural numbers are used to count objects, measure time, and represent quantities such as age, weight, and length.
Also Read: Natural Numbers and Whole Numbers
Natural numbers have several important properties, including being closed under addition, subtraction, and multiplication. This means that when two natural numbers are added, subtracted, or multiplied, the result is always a natural number. However, natural numbers are not closed under division, as the quotient of two natural numbers may be a fraction or a decimal.
Natural numbers are a fundamental concept in mathematics and are used as the basis for many other number systems, including integers, rational numbers, and real numbers. They are used in many different fields, including science, engineering, and economics. The study of natural numbers is an important part of number theory, which is a branch of mathematics that deals with the properties of numbers and their relationships.