What is the atomic number of pt-175 after it undergoes alpha decay

The atomic number of pt-175 after it undergoes alpha decay is 76

Radioactive decay is defined as the splitting of heavy unstable isotopes to two or more stable particles. The three main types of radioactive decay are

An Alpha decay occurs when the radioactive nucleus releases a helium ion (alpha particle) leaving the daughter   nucleus with a  reduced atomic  number by 2 and reduced  atomic mass by  4.  

An example is the alpha decay  below

¹⁷⁵Pt₇₈ >      ¹⁷¹ Os₇₆   + ⁴ He₂

Here,Platinum 175  with atomic number 78 undergoes alpha decay to produce Osmium 171 with atomic number 76.

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76

Explanation:

Alpha decay is one of the most basic forms of radioactive decay. It has an atomic mass of 4 and a proton number of two.

Undergoing an alpha decay will decrease the atomic mass by four and the atomic number by two.

In this particular question, we are particular about the atomic number. The atom has an atomic number of 78. So taking 2 off this gives 76